Disentangling the influence of aridity and salinity on community functional and phylogenetic diversity in local dryland vegetation

Influence of surface water and groundwater on functional traits and trade-off strategies of oasis communities at the end of the Keriya River, China

Plant functional traits reflect the capacity of plants to adapt to their environment and the underlying optimization mechanisms. However, few studies have investigated trade-off strategies for functional traits in desert-wetland ecosystems, the mechanisms by which surface water disturbance and groundwater depth drive functional trait variation at the community scale, and the roles of intraspecific and interspecific variation. Therefore, this study analyzed specific differences in community-weighted mean traits among habitat types and obtained the relative contribution of intraspecific and interspecific variation by decomposing community-weighted mean traits, focusing on the Daliyabuyi Oasis in the hinterland of the Taklamakan Desert. We also explored the mechanisms by which surface water and groundwater influence different sources of variability specifically. The results showed that plant height, relative chlorophyll content, leaf thickness, leaf nitrogen content, and nitrogen-phosphorus ratio were the key traits reflecting habitat differences. As the groundwater depth becomes shallower and surface water disturbance intensifies, plant communities tend to have higher leaf nitrogen content, nitrogen-phosphorus ratio, and relative chlorophyll content and lower height. Surface water, groundwater, soil water content, and total soil nitrogen can influence interspecific and intraspecific variation in these traits through direct and indirect effects. As arid to wet habitats change, plant trade-off strategies for resources will shift from conservative to acquisitive. The study concluded that community functional traits are mainly contributed by interspecific variation, but consideration of intraspecific variation and the covariation effects that exist between it and interspecific variation can help to further enhance the understanding of the response of community traits in desert-wetland ecosystems to environmental change. Surface water disturbance has a non-negligible contribution to this adaptation process and plays a higher role than groundwater depth.

Partitioning and integrating of plant traits and phylogeny in assessing diversity along secondary forest succession in Loess Plateau of China

Assessing plant diversity during community succession based on plant trait and phylogenetic features within a community (alpha scale) and among communities (beta scale) could improve our understanding of community succession mechanism. However, whether changes of community functional diversity at alpha and beta scale are structured by different traits and whether integrating plant traits and phylogeny can enhance the ability in detecting diversity pattern have not been studied in detail. Thirty plots representing different successional stages were established on the Loess Plateau of China and 15 functional traits were measured for all coexisting species. We first analyzed the functional alpha and beta diversity along succession by decomposing species trait into alpha and beta components and then integrated key traits with phylogenetic information to explore their roles in shaping species turnover during community succession. We found that functional alpha diversity increased along successional stages and was structured by morphological traits, while beta diversity decreased during succession and was more structured by stoichiometry traits. Phylogenetic alpha diversity showed congruent pattern with functional alpha diversity because of phylogenetic conservation of trait alpha components (variation within community), while beta diversity showed incongruent pattern due to phylogenetic randomness of trait beta components (variation among communities). Furthermore, only integrating relatively conserved traits (plant height and seed mass) and phylogenetic information can raise the detecting ability in assessing diversity change. Overall, our results reveal the increasing niche differentiation within community and functional convergence among communities with succession process, indicating the importance of matching traits with scale in studying community functional diversity and the asymmetry of traits and phylogeny in reflecting species ecological differences under long-term selection pressures.

Different contributions of plant diversity and soil properties to the community stability in the arid desert ecosystem

As a one of the focuses of ecological research, understanding the regulation of plant diversity on community stability is helpful to reveal the adaption of plant to environmental changes. However, the relationship between plant diversity and community stability is still controversial due to the scale effect of its influencing factors. In this study, we compared the changes in community stability and different plant diversity (i.e., species, functional, and phylogenetic diversities) between three communities (i.e., riparian forest, ecotone community, and desert shrubs), and across three spatial scales (i.e., 100, 400, and 2500 m²), and then quantified the contribution of soil properties and plant diversity to community stability by using structural equation model (SEM) in the Ebinur Lake Basin Nature Reserve of the Xinjiang Uygur Autonomous Region in the NW China. The results showed that: (1) community stability differed among three communities (ecotone community > desert shrubs > riparian forest). The stability of three communities all decreased with the increase of spatial scale (2) species diversity, phylogenetic richness and the mean pairwise phylogenetic distance were higher in ecotone community than that in desert shrubs and riparian forest, while the mean nearest taxa distance showed as riparian forest > ecotone community > desert shrubs. (3) Soil ammonium nitrogen and total phosphorus had the significant direct negative and positive effects on the community stability, respectively. Soil ammonium nitrogen and total phosphorus also indirectly affected community stability by adjusting plant diversity. The interaction among species, functional and phylogenetic diversities also regulated the variation of community stability across the spatial scales. Our results suggested that the effect of plant diversities on community stability were greater than that of soil factors. The asynchronous effect caused by the changes in species composition and functional traits among communities had a positive impact on the stability. Our study provided a theoretical support for the conservation and management of biodiversity and community functions in desert areas.

Impacts of plant and soil stoichiometry on species diversity in a desert ecosystem

Plant and soil stoichiometric ratios can be used to explain changes in the structural and functional characteristics of plant communities. Exploring the relationships between the stoichiometric ratios and plant diversity is helpful to further elucidate the effects of soil and nutrient constraints on community vegetation. However, such studies remain poorly understood in desert ecosystems. In this study, we analysed the effects of soil moisture and salt content on soil and leaf stoichiometry, species diversity and their relationships in the desert ecosystem of the Ebinur Lake basin. The results showed that: (i) Compared with the low soil moisture and salinity (SW2) environment, the soil and leaf C, N, P contents and soil stoichiometric ratios were larger in the high soil moisture and salinity (SW1) environment, and the leaf stoichiometric ratios were smaller. (ii) In SW1 environment, species diversity was negatively correlated with soil C:N and C:P, but weakly correlated with soil stoichiometric ratios in SW2 environment. In addition, the relationships between it and leaf stoichiometric ratios were reversed in different moisture and salinity environments. (iii) Structural equation modelling showed that leaf C:P, C:N and soil C:P had strong effects on species diversity. This research aims to provide a scientific reference for maintaining plant diversity, vegetation reconstruction and ecosystem restoration in desert areas, and enrich the ecological stoichiometric theory of desert ecosystems.

Spatial Scale Effects of Soil Respiration in Arid Desert Tugai Forest: Responses to Plant Functional Traits and Soil Abiotic Factors

Understanding the spatial variation law of soil respiration (Rs) and its influencing factors is very important when simulating and predicting the terrestrial carbon cycle process. However, there are still limitations in understanding how different sampling scales affect the spatial heterogeneity of Rs and whether the spatial scale effect will change with habitat types. Our objectives were to explore the effects of different sampling scales on the spatial variability of Rs and the relative importance of soil abiotic characteristics and plant traits in influencing the spatial variability of Rs. The Rs, soil properties, and plant traits were measured through field investigation and indoor analysis in the Tugai forest desert plant community in the Ebinur Lake Basin in northwest China. The Rs showed significant water gradient changes, with a coefficient of variation of 35.4%–58%. Plot types had significant effects on Rs, while the change of sampling scale did not lead to significant differences in Rs. At the plot scale, Rs spatial variation at the 5 m × 5 m sampling scale mainly depended on plant traits (leaf length, leaf thickness, leaf dry matter content, and leaf phosphorus content, p < 0.05), while Rs spatial variation at the 10 m × 10 m scale mainly depended on soil properties (soil total phosphorus, ammonium nitrogen, soil water content, and pH, p < 0.05). At the local scale, soil nutrients (soil available phosphorus and ammonium nitrogen) and plant traits (maximum plant height, leaf length, and phosphorus content) at the 5 m × 5 m scale jointly explained 49% of the spatial change of Rs. In contrast, soil microclimate (soil water content), soil nutrients (soil pH, available phosphorus, and nitrate nitrogen), and plant traits (leaf thickness) jointly explained 51% of the spatial variation of Rs at the 10 m × 10 m scale. These results demonstrate the potential to predict the spatial variability of Rs based on the combination of easily measured aboveground functional traits and soil properties, which provides new ideas and perspectives for further understanding the mechanism of Rs change in Tugai forests.

Coupled Relationship between Soil Physicochemical Properties and Plant Diversity in the Process of Vegetation Restoration

An in-depth exploration of plant–soil interactions can improve our knowledge of the succession and evolution of forest ecosystems. To understand the coupling relationship between species diversity and soil physicochemical properties in natural secondary forests during the process of vegetation restoration, the species diversity of trees, shrubs and herbs and the physicochemical properties of soil at different depths were investigated in six forest communities in the Qinling Huoditang area over two years (2013 and 2019). The analysis indicated that the soil nutrient content in the region decreased during this period, but the plant diversity index showed no obvious change. Through RDA and regression analysis, we determined that the correlations between plant diversity and soil physicochemical properties were discrete. The tree and herb species diversity were most closely related to the surface soil, while shrub diversity was more strongly regulated by the middle soil layer. Available phosphorus had the strongest effect on trees, and the main factors affecting shrubs were NO3-N and NH4-N. Herb growth was more limited by soil physical properties such as the soil bulk density and porosity. We concluded that evident correlations exist between soil physicochemical properties and plant communities. After six years of natural restoration, the plant diversity index did not change significantly. However, the soil nutrient content decreased obviously. This study provides a reference for the management of vegetation restoration processes in forest ecosystems.

Discriminating ecological processes affecting different dimensions of α‐ and β‐diversity in desert plant communities

Understanding the spatial distribution of plant diversity and its drivers are major challenges in biogeography and conservation biology. Integrating multiple facets of biodiversity (e.g., taxonomic, phylogenetic, and functional biodiversity) may advance our understanding on how community assembly processes drive the distribution of biodiversity. In this study, plant communities in 60 sampling plots in desert ecosystems were investigated. The effects of local environment and spatial factors on the species, functional, and phylogenetic α‐ and β‐diversity (including turnover and nestedness components) of desert plant communities were investigated. The results showed that functional and phylogenetic α‐diversity were negatively correlated with species richness, and were significantly positively correlated with each other. Environmental filtering mainly influenced species richness and Rao quadratic entropy; phylogenetic α‐diversity was mainly influenced by dispersal limitation. Species and phylogenetic β‐diversity were mainly consisted of turnover component. The functional β‐diversity and its turnover component were mainly influenced by environmental factors, while dispersal limitation dominantly effected species and phylogenetic β‐diversity and their turnover component of species and phylogenetic β‐diversity. Soil organic carbon and soil pH significantly influenced different dimensions of α‐diversity, and soil moisture, salinity, organic carbon, and total nitrogen significantly influenced different dimensions of α‐ and β‐diversity and their components. Overall, it appeared that the relative influence of environmental and spatial factors on taxonomic, functional, and phylogenetic diversity differed at the α and β scales. Quantifying α‐ and β‐diversity at different biodiversity dimensions can help researchers to more accurately assess patterns of diversity and community assembly.

Quantifying Leaf Trait Covariations and Their Relationships with Plant Adaptation Strategies along an Aridity Gradient

Simple Summary

Plants usually adopt different strategies to adapt to their surrounding environments. Accurately quantifying plant strategies is of great interest in trait-based ecology, in particular to understand the responses of ecological structures and processes. In the last two decades, these strategies have been described qualitatively; however, the use of quantitative methods is still lacking. In this study, we used a plant functional trait approach to discuss plant strategies along an aridity gradient. We found that eight functional traits divided into four dimensions represent four adaptation strategies: energy balance, resource acquisition, resource investment and water use efficiency. We also concluded that climate and soil together with family (vegetation succession) were the main driving forces of trait covariations. Our study provided a new perspective to understand plant functional responses to aridity gradients, which is helpful for ecological management and vegetation restoration programs in arid regions.

Abstract

A trait-based approach is an effective way to quantify plant adaptation strategies in response to changing environments. Single trait variations have been well depicted before; however, multi-trait covariations and their roles in shaping plant adaptation strategies along aridity gradients remain unclear. The purpose of this study was to reveal multi-trait covariation characteristics, their controls and their relevance to plant adaptation strategies. Using eight relevant plant functional traits and multivariate statistical approaches, we found the following: (1) the eight studied traits show evident covariation characteristics and could be grouped into four functional dimensions linked to plant strategies, namely energy balance, resource acquisition, resource investment and water use efficiency; (2) leaf area (LA) together with traits related to the leaf economic spectrum, including leaf nitrogen content per area (N_area), leaf nitrogen per mass (N_mass) and leaf dry mass per area (LMA), covaried along the aridity gradient (represented by the moisture index, MI) and dominated the trait–environmental change axis; (3) together, climate, soil and family can explain 50.4% of trait covariations; thus, vegetation succession along the aridity gradient cannot be neglected in trait covariations. Our findings provide novel perspectives toward a better understanding of plant adaptations to arid conditions and serve as a reference for vegetation restoration and management programs in arid regions.

The relative contribution of intraspecific variation and species turnover to the community-level foliar stoichiometric characteristics in different soil moisture and salinity habitats

BACKGROUND

Trait-based approaches have been used to demonstrate the responses of plant functional traits to environmental change may manifest both among- and/or within-species. However, how community-level foliar stoichiometric characteristic variations respond to aridity and salinity is still not well-known.

METHODS

We calculated community weighted means (CWMs) and non-weighted means (CMs) of foliar C, N, and P concentrations (and their ratios) in a dryland plant community respond to high (HSW) and low soil moisture and salinity (LSW). Based on a sum of squares decomposition method, we determined the relative contributions of intraspecific variation and species turnover in both HSW and LSW habitats.

RESULTS

The CWMs of foliar C, C:N and C:P, and CM of N in the HSW habitat were significantly greater than those in the LSW habitat. The trait variations in two habitats were mainly driven by intraspecific variation, and its contribution to trait variation mostly declined with the decrease of soil moisture and salinity. The CWMs of foliar C-related stoichiometric characteristics were mainly dominated by species turnover in both habitats. Moreover, the contribution of species turnover to C and C:P variations showed an increasing trend in the LSW habitat. For CWMs, negative covariations between intraspecific variation and turnover occurred in HSW and positive covariations (except N:P) occurred in LSW; however, CMs were generally positively correlated in both habitats.

CONCLUSIONS

The intraspecific variation declined as drought stress intensified, which indicates that the adaptability of desert plants declined when the stress changed from salinity to aridity. The total variation of C-related traits in both habitats were mainly dominated by species turnover. These findings highlight the importance of intraspecific variation in driving desert plant response of community functional composition to salt stress, and the joint role of intraspecific variation and species turnover in resisting drought stress.

Factors that alter the relative importance of abiotic and biotic drivers on the fertile island in a desert-oasis ecotone

Dryland vegetation forms a "fertile island effect" due to water and nutrient retention. However, there has been little research on the mechanism underlying C-, N-, P-accumulation and overall fertile island at the community level. We therefore presented the systematic investigation on this issue through the survey in desert-oasis ecotone. The survey covering the vegetation composition, plant height, crown area and vegetation cover. The main parameters measured included soil moisture, soil pH, soil salinity and nine soil indicators related to C, N and P cycling. The results revealed that the effect of fertile island was directly relevant to either soil moisture or pH. This effect was more obvious with the increase of soil moisture and the decrease of pH value. In addition, the plant diversity was believed to be the main biotic driven factor for fertile island. Furthermore, the results also indicated that both the soil moisture and plant diversity would accelerate the accumulation of P and N, while the pH played the negative effect. The other main observation obtained was that the vegetation cover had positive effect on accumulation of C. As a result, the mechanisms related to drought and salinization could drive the difference of C-, N- and P-accumulation. The main findings also provided an effective reference to better understand the mechanism of fertile island and its desertification procedure in desert-oasis ecotone.