Nitrogen effects on grassland biomass production and biodiversity are stronger than those of phosphorus

Synergistic interplay of management practices and environmental factors in shaping grassland soil carbon stocks: Insights into the effects of fertilization, mowing, burning, and grazing

Grasslands, which account for over 40 % of the Earth's terrestrial area, play a vital role in mitigating global change and biodiversity loss. These ecosystems serve as critical carbon sinks, regulating the global carbon cycle and supporting diverse flora and fauna. However, their ability to sustain these functions is threatened by land use change and climate disruption. Current challenges revolve around understanding how key management practices such as grazing, mowing, burning, and fertilization, interact with environmental factors to influence grassland soil carbon stocks. This study presents a meta-analysis of the effects of these management practices and environmental factors, such as soil type, depth, texture, temperature, precipitation, and their synergistic interplay. It evaluates how management intensity, duration, and frequency interact with these environmental variables to influence soil carbon storage, providing valuable insights into optimizing grassland management for enhanced soil carbon stock and broader ecosystem stability. The findings reveal that grazing, particularly at high intensity, tends to reduce soil carbon stocks (-0.412, p < 0.001), with the most pronounced effects observed in shallow soils and temperate climates. Mowing also negatively affected carbon stock (-0.416, p = 0.013), especially when carried out frequently and over long durations. On the other hand, burning had mixed results with an overall positive effect (0.340, p = 0.078). Short-term burns promoted carbon accumulation, while frequent burning led to carbon loss. Fertilization, especially with nitrogen and phosphorus, proved beneficial for increasing soil carbon stocks (0.712, p < 0.001), particularly in nutrient-poor soils and semi-arid climates. This study introduces a systems-based approach to grassland management, providing a framework for optimizing carbon-focused strategies. By integrating the role of management practices, particularly their frequency, intensity, and duration, along with soil characteristics and climate, these findings provide actionable insights for policymakers, land managers, and researchers. They guide the development of sustainable management strategies that not only enhance soil carbon stocks but also support ecosystem health and resilience.

Plants and soil biota co-regulate stability of ecosystem multifunctionality under multiple environmental changes

The increase in phosphorus (P) and nitrogen (N) inputs, as well as soil acidification resulting from multiple environmental changes, has profound effects on the attributes of plant and soil biota communities, and on ecosystem functions. However, how these community attributes impact ecosystem multifunctionality (EMF) and its stability under multiple environmental changes remains unclear. By integrating datasets over four consecutive years from an experiment with enrichments of soil acidification and N and P in a semiarid grassland on the Mongolian Plateau, we explored the effects of environmental changes on community attributes (species richness, asynchrony, and compositional temporal stability) of plants and soil biota (bacteria, fungi, and nematodes) and their associations with EMF stability. The attributes of plants and soil biota showed opposite responses to nutrient enrichment under soil acidification and non-acidification conditions. Soil acidification had a more significant effect on the community attributes of plants and soil biota, as well as on the components of EMF stability, than nutrient enrichment. Soil acidification decreased both the mean and stability of EMF, while N enrichment increased the mean of EMF. P did not have a significant effect on the components of EMF stability, but N and P showed positive interactive effects on the mean and stability of EMF. We also found that plant and soil biota richness had a positive effect on EMF, while plant asynchrony and soil biota compositional stability determined EMF stability. The community attributes of plants and soil biota co-regulate the components of EMF stability under multiple environmental changes. These findings highlight the urgent need to protect the biodiversity of plants and soil biota to maintain EMF and its stability, especially for ecosystems undergoing multiple environmental changes.

Optimization of nitrogen and phosphorus fertilization for enhanced forage production and quality of Festuca Krylovianacv. Huanhu artificial grassland in alpine regions

Artificial grasslands of F. kryloviana in the region surrounding Qinghai Lake have been observed to a decline in productivity following three years of establishment. Traditional fertilization practices, aimed at maintaining ecological balance, have predominantly focused on the application of phosphorus. However, it remains unclear whether phosphorus fertilizers offer a superior advantage over nitrogen fertilizers in sustaining productivity. Consequently, from 2017 to 2019, we conducted an experimental to assess the impact of nitrogen and phosphorus fertilization on forage yield and quality. We designed with four levels of phosphorus and two levels of nitrogen, resulting in eight distinct fertilizer combinations. Our experimental findings indicate that the degradation of artificial grasslands leads to a shift in the allocation pattern of aboveground biomass. There was a respective decrease of 68.2 % and 62.5 % in the biomass proportions of stems and ears, contrasted by a greater than 200 % increase in the biomass proportion of leaves. The application of nitrogen not only elevated the total aboveground biomass but also promoted a preferential allocation of biomass to stems and leaves, consequently enhancing the forage's crude protein content. Nitrogen fertilization significantly increased aboveground biomass, and crude protein content by 63.21 %, and 6 %, respectively. Phosphorus fertilization's impact varied annually but favored the distribution of biomass to stems and ears. The net photosynthetic rate improved by over 53.12 % with fertilizer application, although the differences among treatments were not statistically significant. The balanced application of nitrogen and phosphorus fertilizers significantly bolstered the aboveground biomass, ear biomass, stem biomass, leaf biomass, and crude protein content in varying years by 17.25 %-209.83 %, 34.7 %-438.9 %, 25.5 %-250.2 %, 18.4 %-133.3 %, and 10.21 %-25.62 %, respectively. Our analysis revealed that nitrogen-only fertilization exhibited the most optimal fertilizer use efficiency and economic returns. In conclusion, nitrogen fertilization is crucial for sustaining the productivity and quality of F. kryloviana artificial grasslands. The local practice of 75 kg ha-1 phosphorus fertilizer is detrimental to the maintenance of productivity in F. kryloviana artificial grasslands. This study offers valuable insights into the optimization of fertilization strategies for sustainable forage production within alpine regions.

Functional Groups Dominate Aboveground Net Primary Production under Long-Term Nutrient Additions in a Tibetan Alpine Meadow

Anthropogenic nutrient additions are influencing the structure and function of alpine grassland ecosystems. However, the underlying mechanisms of the direct and indirect effects of nutrient additions on aboveground net primary productivity (ANPP) are not well understood. In this study, we conducted an eight-year field experiment to explore the ecological consequences of nitrogen (N) and/or phosphorous (P) additions on the northern Tibetan Plateau. ANPP, species diversity, functional diversity, and functional groups were used to assess species' responses to increasing nutrients. Our results showed that nutrient additions significantly increased ANPP due to the release in nutrient limitations. Although N addition had a significant effect on species richness and functional richness, and P and N + P additions altered functional diversity, it was functional groups rather than biodiversity that drove changes in ANPP in the indirect pathways. We identified the important roles of N and P additions in begetting the dominance of grasses and forbs, respectively. The study highlights that the shift of functional groups should be taken into consideration to better predict the structure, function, and biodiversity-ANPP relationship in grasslands, particularly under future multifaceted global change.

Asymmetric response of aboveground and belowground temporal stability to nitrogen and phosphorus addition in a Tibetan alpine grassland

Anthropogenic eutrophication is known to impair the stability of aboveground net primary productivity (ANPP), but its effects on the stability of belowground (BNPP) and total (TNPP) net primary productivity remain poorly understood. Based on a nitrogen and phosphorus addition experiment in a Tibetan alpine grassland, we show that nitrogen addition had little impact on the temporal stability of ANPP, BNPP, and TNPP, whereas phosphorus addition reduced the temporal stability of BNPP and TNPP, but not ANPP. Significant interactive effects of nitrogen and phosphorus addition were observed on the stability of ANPP because of the opposite phosphorus effects under ambient and enriched nitrogen conditions. We found that the stability of TNPP was primarily driven by that of BNPP rather than that of ANPP. The responses of BNPP stability cannot be predicted by those of ANPP stability, as the variations in responses of ANPP and BNPP to enriched nutrient, with ANPP increased while BNPP remained unaffected, resulted in asymmetric responses in their stability. The dynamics of grasses, the most abundant plant functional group, instead of community species diversity, largely contributed to the ANPP stability. Under the enriched nutrient condition, the synchronization of grasses reduced the grass stability, while the latter had a significant but weak negative impact on the BNPP stability. These findings challenge the prevalent view that species diversity regulates the responses of ecosystem stability to nutrient enrichment. Our findings also suggest that the ecological consequences of nutrient enrichment on ecosystem stability cannot be accurately predicted from the responses of aboveground components and highlight the need for a better understanding of the belowground ecosystem dynamics.

An open-access global database of meta-analyses investigating yield and biodiversity responses to different management practices

We here present a database of evidence on the impact of agricultural management practices on biodiversity and yield. This database is the result of a systematic literature review, that aimed to identify meta-analyses that use as their response variables any measure of biodiversity and yield. After screening more than 1,086 titles and abstracts, we identified 33 relevant meta-analyses, from which we extracted the overall estimates, the subgroup estimates as well as all information related to them (effect size metric, taxonomic group, crop type etc.). We also extracted information relative to the empirical studies used for each meta-analysis and recorded the countries in which they took place and assessed the quality of each meta-analysis. Our dataset is publicly accessible and can be used for conducting second-order meta-analyses on the effect of management measures on species richness, taxon abundance, biomass and yields. It can also be used to create evidence maps on agriculture-related questions.

Higher N Addition and Mowing Interactively Improved Net Primary Productivity by Stimulating Gross Nitrification in a Temperate Steppe of Northern China

Anthropogenic disturbance, such as nitrogen (N) fertilization and mowing, is constantly changing the function and structure of grassland ecosystems during past years and will continue to affect the sustainability of arid and semiarid grassland in the future. However, how and whether the different N addition levels and the frequency of N addition, as well as the occurrence of mowing, affect the key processes of N cycling is still unclear. We designed a field experiment with five levels of N addition (0, 2, 10, 20, and 50 g N m-2 yr-1), two types of N addition frequencies (twice a year added in June/November and monthly addition), and mowing treatment in a typical grassland of northern China. The results showed that higher N addition and mowing interactively improved net primary productivity (NPP), including aboveground and belowground biomass, while different N addition frequency had no significant effects on NPP. Different N addition levels significantly improved gross ammonification (GA) and nitrification (GN) rates, which positively correlated to aboveground net primary productivity (ANPP). However, the effect of N addition frequency was differentiated with N addition levels, the highest N addition level (50 g N m-2 yr-1) with lower frequency (twice a year) significantly increased GA and GN rates. Mowing significantly increased the GA rate but decreased the GN rate both under the highest N addition level (50 g N m-2 yr-1) and lower N addition frequency (twice a year), which could improve N turnover by stimulating plant and microbial activity. However, a long-term study of the effects of N enrichment and mowing on N turnover will be needed for understanding the mechanisms by which nutrient cycling occurs in typical grassland ecosystems under global change scenarios.

Co-limitation of N and P is more prevalent in the Qinghai-Tibetan Plateau grasslands

Introduction

Over the past three decades, the view of nutrient limitation has transferred from single-nutrient limitation to multiple-nutrient limitation. On the Qinghai-Tibetan Plateau (QTP), many nitrogen (N) and phosphorus (P) addition experiments have revealed different N- or P-limited patterns at many alpine grassland sites, whereas it is not clear what the general patterns of N and P limitation across the QTP grasslands.

Methods

We performed a meta-analysis, containing 107 publications, to assess how N and P constrained plant biomass and diversity in alpine grasslands across the QTP. We also tested how mean annual precipitation (MAP) and mean annual temperature (MAT) influence N and P limitations.

Results

The findings show that plant biomass in QTP grasslands is co-limited by N and P. Single N limitation is stronger than single P limitation, and the combined positive effect of N and P addition is stronger than that of single nutrient additions. The response of biomass to N fertilization rate shows an increase firstly and then declines, and peaks at approximately 25 g N·m-2·year-1. MAP promotes the effect of N limitation on plant aboveground biomass and diminishes the effect of N limitation on belowground biomass. Meanwhile, N and P addition generally decline plant diversity. Moreover, the negative response of plant diversity to N and P co-addition is strongest than that of single nutrient additions.

Discussion

Our results highlight that N and P co-limitation is more prevalent than N- or P-limitation alone in alpine grasslands on the QTP. Our findings provide a better understanding of nutrient limitation and management for alpine grasslands on the QTP.