PJB-2019-575
Divergent responses of nitrogen and phosphorus resorption efficiency to nitrogen enrichment in an alpine grassland of Central Asia
yuan su
Abstract
Increasing nitrogen (N) deposition is major driver of global changes that are expected to influence plant nutrient resorption in alpine grassland ecosystems, where plant growth is often nutrient limited. However, knowledge on the effects of increased N deposition on it remain poorly understood. Nutrient resorption (NR) plays a key driver in plant nutrient conservation. Accordingly, nutrient resorption patterns have ecological implications for ecosystem nutrient cycling. In an alpine grassland in northwestern China, we investigated the effects of various N application rates on nutrient concentrations and resorption at species levels of two dominant and perennial grasses, Leymus tiansecalinus and Festuca ovina, taking advantage of a field experiment that has been running for10 years. After10 years of treatments, available N in soil and N concentrations and N:P ratios in mature and senesced leaves increased with increasing rates of N addition. P concentrations in mature and senesced leaves and N resorption significantly decreased along the N addition gradient, but increased P resorption. The divergence of N and P resorption in response to N deposition emphasizes the importance of NR as a pathway by which plants adjust to increasing N availability. The N:P resorption ratios decreased along the N addition gradient, indicating the sensitivity of plant N and P stoichiometry to N addition. Regression analyses showed that soil N available and plant available N:P ratios are important determinants in regulating N and P concentrations and resorption patterns for both grass species. The N:P resorption ratios for both species were significantly negatively related to plant available N:P ratios in soil, suggesting that the changes in N:P resorption ratios did not not simply result from changes in N or P availability. Our results suggested that N addition may partly mitigate nitrogen constraint and exacerbated the P limitation to grass growth. The divergence of N and P resorption to N addition emphasizes that NR is sensitive to nutrient addition and is an important nutrient conservation strategy for alpine grasslands ecosystem under global environmental changes. Collectively, these results suggested that N addition may also lead to decoupling of nitrogen and phosphorus in plants. Thus, enhancing N deposition would likely change plant community composition and primary productivity by the indirect influences on nutrient cycling.
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