Drought and warming alter gross primary production allocation and reduce productivity in a widespread pasture grass

Spatial evolutionary public goods game theory applied to optimal resource allocation and defense strategies in herbaceous plants

Empirical evidence suggests that the attractiveness of a plant to herbivores can be affected by the investment in defense by neighboring plants, as well as investment in defense by the focal plant. Thus, the payoff for allocating to defense may not only be influenced by the frequency and intensity of herbivory but also by defense strategies employed by other plants in the environment. We use a combination of spatial evolutionary game theory and stochastic dynamic programming to predict the proportion of plants in the population investing in defense (cooperators) and the proportion of plants that do not (defectors). Our model accounts for metabolic costs of maintenance of stored resources when predicting optimal resource allocation to growth, reproduction, and storage; this cost is not commonly accounted for in previous models. For both annual and perennial plants, our model predicts an evolutionarily stable proportion of cooperators and defectors (mixed stable strategy), but the proportion of cooperators is higher in a population of perennial plants than in a population of annual plants. We also show that including a metabolic cost of maintaining stored resources does not change the proportion of cooperators but does decrease plant fitness and allocation to overwinter storage.

Soil heterotrophic respiration repressed by drought stress more than soil autotrophic respiration in Stipa breviflora desert steppe, China

Quantification of soil carbon emissions in desert steppes is a key issue in determining the carbon budget in arid regions. However, the changes in and driving mechanisms of soil respiration and its components in response to drought in ecosystems under long-term water stress remain unclear. In this study, rain reduction by 30% and 50% experiments were conducted to simulate drought during the growing season in 2023 in the Stipa breviflora desert steppe. Total soil respiration and soil heterotrophic respiration were measured, and simultaneously, the surface soil temperature and moisture were measured at 0-10 cm. Surface soil microorganisms, microbial biomass carbon, and enzymatic activity were also tested. The results showed that drought significantly decreased soil microbial biomass carbon and enzymatic activity, but had no significant effects on soil microbial richness and diversity, as well as the dominant flora. The inhibitory effect of drought on soil autotrophic respiration only appeared at the beginning of the growing season and then disappeared with plant growth because of the drought-resistant ability of perennial plants in the desert steppe. Heterotrophic respiration is the primary soil carbon release process occurring in the desert steppe, approximately four times that of autotrophic respiration. Soil temperature and moisture jointly regulated heterotrophic respiration under extreme drought conditions (rainfall reduction of 50%); however, their influence on autotrophic respiration became insignificant. This study indicates that drought slowed the decomposition of soil organic carbon and had a weak effect on plant root respiration in the S. breviflora desert steppe. The response process of Rs and its components to drought stress provided theoretical basis for soil carbon feedback in desert steppe under extreme drought conditions.

Preferential Carbon Allocation Into Vegetative Ramets and Belowground Organs During the Seed-Filling Stage Limits Seed Set in Leymus chinensis

Clonal perennial grasses are the dominant species in almost all natural grasslands, however their seed production is typically low. The reasons why seed set is so low remains unclear. We studied a rhizomatous grass (Leymus chinensis) using 13C tracing the different photosynthetic organs to investigate carbon fixation and allocation during the seed-filling stage. We found that the vegetative ramet leaves are the largest (81%) source for total plant fixed carbon, whereas almost all carbon is allocated to vegetative reproduction. The spike is the largest (54%) carbon source for the seeds. However, the spike produced carbon only allocated 37% to the seeds, with the majority allocated to vegetative reproduction. This preferential carbon allocation to vegetative reproduction limits sexual reproduction. Nitrogen application significantly increased assimilated carbon. However, nearly all increased carbon accumulated in the vegetative reproduction rather than in the seeds. Only the carbon produced by the spike increased its allocation to the seeds by 13%. Taken together, we conclude that the predominance of vegetative reproduction, combined with self-incompatibility, results in low ovule fertilization and very weak seed sink strength for carbon competition, suggests that the weak seed sink strength is the key reason causing low seed set in L. chinensis.

Light intensity moderates photosynthesis by optimizing photosystem mechanisms under high VPD stress

In recent decades, the global increase in vapor pressure deficit (VPD) has significantly inhibited plant growth and photosynthesis. Light intensity, a crucial environmental regulator, plays a vital role in stress response and photosynthetic adjustment. This study investigated whether increasing light intensity under high VPD conditions could optimise the photosystem and thereby enhance photosynthesis. We designed experiments using factorial combinations of two VPD levels (HVPD; high VPD, AVPD; appropriate VPD) and two irradiance gradients (L300; 300 μmol photons m-2 s-1, L600; 600 μmol photons m-2 s-1). Under high VPD, plants protect their photosystems by reducing light energy absorption and limiting photosynthetic electron flow, which results in reduced photosynthesis. However, when exposed to HVPD + L600, plants exhibited increased light energy absorption, as evidenced by elevated chlorophyll b and carotenoid levels, enhanced response to irradiance, and decreased NPQ and Y(NO). This regimen also enhanced photosynthetic electron transport by increasing the total driving force and plastoquinone pool, consequently improving the photochemical efficiency of the photosystem and ultimately boosting the net photosynthetic rate by 46.9%. This study confirmed that modulating light intensity under high VPD stress can improve photosynthesis by optimizing the photosystem. This novel approach can be utilized to enhance tomato production in arid regions.

Drought and warming interaction cause substantial economic losses in the carbon market potential of China's northern grasslands

Grasslands are being threatened by global drought and warming. Economic assessments of changing grassland carbon sequestration, a prerequisite for nature-based climate-change mitigation policies, are limited when researchers inadequate consider interactions between drought and warming. Here, we quantified the responses of 35 grass biomasses to combined drought and warming, based on manipulation experiments from 34 peer-reviewed papers; subsequently, we matched them with grasslands in northern China-the eastern range of the larger Eurasian Steppe-and further projected the economic implications for carbon market trading and carbon-sequestration costs. The results show that carbon sequestration in all grassland types, except for forbrich steppe, was significantly reduced by the synergistic interactions of drought and warming. Approximately 10 % of the grasslands in central Xinjiang, identified as forbrich steppe, showed resilience to these stressors. In contrast, the rest of northern China's grasslands suffered increased carbon losses due to drought and warming. The combined effects of drought and warming have caused a loss of 1.6 × 104 million Chinese yuan (CNY) in revenue and excess carbon-sequestration costs exceeding 1.1 × 105 million CNY. Overall, our study results indicate that the synergistic effects of drought and warming significantly undermine the economic viability of carbon sequestration in most of northern China's grasslands. As climate change intensifies, understanding and incorporating the complex interactions of drought and warming can aid in the sustainable management of grassland ecosystems and the development of effective climate-change mitigation policies in arenas, including carbon markets.

Amplified photosynthetic responses to drought events offset the positive effects of warming on arid desert plants

Ongoing warming will influence plant photosynthesis via thermal effects and by enhancing water deficit. As the primary limiting factor for the growth and development of plants in arid deserts, water may alter the potential warming effects on plant photosynthesis and lead to increased uncertainty in plant dynamics. Here, we used open-top chambers (OTCs) to evaluate the impacts of in situ warming (+0.5 and +1.5 °C) on the photosynthesis and growth of two representative desert plants, Artemisia ordosica and Grubovia dasyphylla, from wet to dry spells. The plant traits associated with photosynthetic diffusive and biochemical processes were also measured to explore the underlying mechanisms involved. We found that warming significantly increased the net photosynthetic rate (Anet) during wet spells under 1.5 °C warming in both plants, while only increased that of A. ordosica under 0.5 °C warming. During dry spells, Anet decreased both in A. ordosica and G. dasyphylla, with the rates of declining being 48 % and 41 %, respectively, higher than control under warming. Consequently, warming significantly amplified photosynthetic responses to drought events, which offset the positive warming effects during wet spells and led to unchanged plant biomass in both species. Besides, alterations in plant traits tended to be associated with positive warming effects during wet spells, and the negative effects of drought were mainly due to stomatal limitation. Our results emphasised that the potential benefits of warming during wet spells may be reversed during drought events. Thus, the adverse effects of ongoing warming on desert productivity may increase during dry spells in growing seasons and during dry years.

Asymmetric Warming of Day and Night Benefits the Early Growth of Acer mono Seedlings More Than Symmetric Warming

Asymmetric warming refers to the difference between the increase in daytime maximum temperature and the increase in nighttime minimum temperature and has been documented in temperate regions. However, its impacts on seedling growth have been largely ignored. In this study, seedlings of a widely distributed tree species, Acer mono Maxim., were exposed to both symmetric warming (SW) and asymmetric warming scenarios (day warming [DW], night warming [NW] and diurnal asymmetric warming [DAW]). Compared to control, all warming scenarios were found to enhance belowground biomass. DW promoted the seedling growth, while NW reduced the stem biomass. DAW did not impact the total biomass relative to the control. Compared to SW, DAW advanced phenology, increased indole-3-acetic acid content and chlorophyll content, which enhanced total biomass and stored more NSC in the root. Future DAW would be not beneficial to the growth of A. mono seedlings by comparing with the control. This research encourages further exploration of tree growth experiments under asymmetric warming conditions, as most studies tend to underestimate the warming effects on plant growth by focusing on SW. Incorporating the responses of seedling physiology and growth to non-uniform diurnal warming into earth system models is crucial for more accurately predicting carbon and energy balances in a warmer world.

Trade-off in the partitioning of recent photosynthate carbon under global change

There may be trade-offs in the allocation patterns of recent photosynthetic carbon (RPC) allocation in response to environmental changes, with a greater proportion of RPC being directed towards compartments experiencing limited resource availability. Alternatively, the allocation of RPC could shift from sources to sinks as plants processing excess photosynthates. It prompts the question: Does the pattern of RPC allocation vary under global changes? If so, is this variation driven by optimal or by residual C allocation strategies? We conducted a meta-analysis by complicating 273 pairwise observations from 55 articles with 13 C or 14 C pulse or continuous labeling to assess the partitioning of RPC in biomass (leaf, stem, shoot, and root), soil pools (soil organic C, rhizosphere, and microbial biomass C) and CO2 fluxes under elevated CO2 (eCO2 ), warming, drought and nitrogen (N) addition. We propose that the increased allocation of RPC to belowground under sufficient CO2 results from the excretion of excess photosynthates. Warming led to a significant reduction in the percentage of RPC allocated to shoots, alongside an increase in roots allocation, although this was not statistically significant. This pattern is due to the reduced water availability resulting from warming. In conditions of drought, there was a notable increase in the partitioning of RPC to stems (+7.25%) and roots (+36.38%), indicative of a greater investment of RPC in roots for accessing water from deeper soil. Additionally, N addition led to a heightened allocation of RPC in leaves (+10.18%) and shoots (+5.78%), while reducing its partitioning in soil organic C (-8.92%). Contrary to the residual C partitioning observed under eCO2 , the alterations in RPC partitioning in response to warming, drought, and N supplementation are more comprehensively explained through the lens of optimal partitioning theory, showing a trade-off in the partitioning of RPC under global change.

Interactive effects of elevated temperature and drought on plant carbon metabolism: A meta-analysis

Elevated temperature (T_e ) and drought often co-occur and interactively affect plant carbon (C) metabolism and thus the ecosystem C cycling; however, the magnitude of their interaction is unclear, making the projection of global change impacts challenging. Here, we compiled 107 journal articles in which temperature and water availability were jointly manipulated, and we performed a meta-analysis of interactive effects of T_e and drought on leaf photosynthesis (A_growth ) and respiration (R_growth ) at growth temperature, nonstructural carbohydrates and biomass of plants, and their dependencies on experimental and biological moderators (e.g., treatment intensity, plant functional type). Our results showed that, overall, there was no significant interaction of T_e and drought on A_growth . T_e accelerated R_growth under well-watered conditions rather than under drought conditions. The T_e  × drought interaction on leaf soluble sugar and starch concentrations were neutral and negative, respectively. The effect of T_e and drought on plant biomass displayed a negative interaction, with T_e deteriorating the drought impacts. Drought induced an increase in root to shoot ratio at ambient temperature but not at T_e . The magnitudes of T_e and drought negatively modulated the T_e  × drought interactions on A_growth . Root biomass of woody plants was more vulnerable to drought than that of herbaceous plants at ambient temperature, but this difference diminished at T_e . Perennial herbs exhibited a stronger amplifying effect of T_e on plant biomass in response to drought than did annual herbs. T_e exacerbated the responses of A_growth and stomatal conductance to drought for evergreen broadleaf trees rather than for deciduous broadleaf and evergreen coniferous trees. A negative T_e  × drought interaction on plant biomass was observed on species-level rather than on community-level. Collectively, our findings provide a mechanistic understanding of the interactive effects of T_e and drought on plant C metabolism, which would improve the prediction of climate change impacts.

Belowground carbon allocation, root trait plasticity, and productivity during drought and warming in a pasture grass

Sustaining grassland production in a changing climate requires an understanding of plant adaptation strategies, including trait plasticity under warmer and drier conditions. However, our knowledge to date disproportionately relies on aboveground responses, despite the importance of belowground traits in maintaining aboveground growth, especially in grazed systems. We subjected a perennial pasture grass, Festuca arundinacea, to year-round warming (+3 °C) and cool-season drought (60% rainfall reduction) in a factorial field experiment to test the hypotheses that: (i) drought and warming increase carbon allocation belowground and shift root traits towards greater resource acquisition and (ii) increased belowground carbon reserves support post-drought aboveground recovery. Drought and warming reduced plant production and biomass allocation belowground. Drought increased specific root length and reduced root diameter in warmed plots but increased root starch concentrations under ambient temperature. Higher diameter and soluble sugar concentrations of roots and starch storage in crowns explained aboveground production under climate extremes. However, the lack of association between post-drought aboveground biomass and belowground carbon and nitrogen reserves contrasted with our predictions. These findings demonstrate that root trait plasticity and belowground carbon reserves play a key role in aboveground production during climate stress, helping predict pasture responses and inform management decisions under future climates.

Soil and water conservation measures to adapt cropping systems to climate change facilitated water stresses in Africa

Complex controls and non-linear responses of the climate system to global warming make it difficult to have clear-cut predictions of future precipitation amounts and timelines. It is, however, evident from current observations that some predictions of unusually high rates of flooding and droughts are occurring and threatening food security in sub-Saharan Africa (SSA). The impact of climate change is immense on SSA though it contributes the least to climate change globally. Crops face lots of growth challenges which reduce their productivity under drought and flood conditions. SSA must prepare agricultural soils for the anticipated climate variabilities, to ensure sustainable food availability. The effort to adapt soils to climate change must be a concerted one, using technologies from various facets of science. Stakeholders must adopt water-smart strategies that maintain proper soil-water balance. They should focus on manageable inherent soil properties that control the susceptibility/adaptability of cropping systems to climate change. Conservation agriculture techniques that target improving soil organic matter and maintaining soil life; protecting the soil from compaction and erosion; reducing soil disturbance; enhancing soil infiltration and groundwater recharge capacity, must be applied to our soils. A number of these techniques equip the soils to be better sinks of excess water in flood-prone areas and improve water-holding capacities in drought-prone ones. Governments, farmers, and all stakeholders must also invest in both simple and complex water harvesting/ re-directing infrastructure which conserve water for future use. Water-efficient irrigation systems must be employed by farmers during water scarcity. Most importantly, gaps between research, industry, farmers, and governments must be bridged to for easy flow of information on improved technologies and quick adoption of climate change mitigation strategies.