State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shaanxi 712100, China; University of Chinese Academy of Sciences, Beijing 100049, China; Institute of Geographical Sciences, Henan Academy of Sciences, Zhengzhou, Henan 450052, China.
State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, Shaanxi 712100, China.
Sci Total Environ. 2022 Jul 20;831:154807. doi: 10.1016/j.scitotenv.2022.154807. Epub 2022 Mar 24.
Global warming and nitrogen (N) deposition are known to unbalance the stoichiometry of carbon (C), N, and phosphorus (P) in terrestrial plants, but it is unclear how water availability regulates their effects along a natural aridity gradient. Here, we conducted manipulative experiments to determine the effects of experimental warming (WT) and N addition (NT) on plant stoichiometry in desert, typical, and meadow steppes with decreasing aridity. WT elevated air temperatures by 1.2-2.9 °C using open-top chambers. WT increased forb C:N ratio and thus its N use efficiency and competitiveness in desert steppes, whereas WT reduced forb C:N and C:P ratios in typical and meadow steppes. Plant N:P ratio, which reflects nutrient limitation, was reduced by WT in desert steppes but not for typical or meadow steppes. NT reduced plant C:N ratios and increased N:P ratios in all three steppes. NT reduced forb C:P ratios in desert and typical steppes, but it enhanced grass C:P ratio in meadow steppes, indicating an enhancement of P use efficiency and competitiveness of grasses in wet steppes. WT and NT had synergetic effects on grass C:N and C:P ratios in all three steppes, which helps to increase grasses' productivity. Under WT or NT, the changes in community C:N ratio were positively correlated with increasing aridity, indicating that aridity increases plants' N use efficiency. However, aridity negatively affected the changes in N:P ratios under NT but not WT, which suggests that aridity mitigates P limitation induced by N deposition. Our results imply that warming could shift the dominant functional group into forbs in dry steppes due to altered stoichiometry, whereas grasses become dominated plants in wet steppes under increasing N deposition. We suggest that global changes might break the stoichiometric balance of plants and water availability could strongly modify such processes in semi-arid steppes.
全球变暖与氮（N）沉降被认为会打破陆地植物碳（C）、N 和磷（P）的化学计量平衡，但水分可利用性如何在自然干旱梯度上调节这些效应还不清楚。在这里，我们进行了操纵实验，以确定实验增温（WT）和 N 添加（NT）对干旱程度依次降低的荒漠、典型与草甸草原植物化学计量的影响。使用开顶式气室，WT 将空气温度升高了 1.2-2.9°C。WT 提高了荒漠草原植物的 C:N 比，从而提高了其 N 利用效率和竞争力，而 WT 降低了典型和草甸草原植物的 C:N 和 C:P 比。反映养分限制的植物 N:P 比在荒漠草原因 WT 而降低，但在典型或草甸草原则没有。NT 降低了所有三种草原植物的 C:N 比，并增加了 N:P 比。NT 降低了荒漠和典型草原植物的 C:P 比，但增强了草甸草原植物的 C:P 比，表明湿草原植物 P 利用效率和竞争力提高。WT 和 NT 对所有三种草原的植物 C:N 和 C:P 比具有协同效应，有助于提高植物生产力。在 WT 或 NT 下，群落 C:N 比的变化与干旱度的增加呈正相关，表明干旱度提高了植物的 N 利用效率。然而，干旱度对 NT 下 N:P 比的变化有负面影响，但对 WT 下则没有，这表明干旱度减轻了 N 沉降引起的 P 限制。我们的研究结果表明，由于化学计量的改变，增温可能会使干旱草原的优势功能群转变为草本植物，而在 N 沉降增加的情况下，草本植物则成为优势植物。我们认为，全球变化可能会打破植物的化学计量平衡，而水分可利用性可以强烈改变半干旱草原的这些过程。
