Responses of two contrasting saline-alkaline grassland communities to nitrogen addition during early secondary succession (10.1111/jvs.12282)
Responses of two contrasting saline-alkaline grassland communities to nitrogen addition during early secondary succession (10.1111/jvs.12282)
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两个对比鲜明的盐碱草原群落在次生演替早期对氮添加的响应 (10.1111/jvs.12282)
DOI：
10.1111/jvs.12282
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通讯作者：
Chunsheng Mu
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作者：
Zhenjian Bai;Ying Gao;Fu Xing;Shengnan Sun;Deyu Jiao;Xiuhong Wei;Chunsheng Mu
问题（1）在半干旱地区的高盐碱和低盐碱草地群落中，次生演替动态有何不同？（2）在盐碱胁迫下，氮（N）富集是否促进植物次生演替？LocationSaline-alkaline grassland in northeast China.MethodsWe selected two early succession communities different in soil saline-alkaline stress and floric composition：one 'high-stress community' co-dominated by annual grass Chloris virgata and annual forbs Artemisia scoparia and Kochia sieversiana，and one 'low-stress community' dominated by annual forbK. sieversiana.连续4年（2008-2011年）进行了5个氮添加水平的完全随机设计试验，重复3次。每年对植被变量（单个物种的地上生物量、功能群、群落水平、群落物种丰富度）和土壤特性（pH值、电导率作为盐度的代表）进行调查。去趋势对应分析（DCA）被用来评估演替trajectors.ResultsDCA揭示了两个社区之间的物种组成和演替轨迹的明显差异。高应力群落的物种组成变化不大，在4年的时间里，一年生物种在所有地块中占主导地位。然而，大多数低应力群落从一年生主导阶段发展到多年生主导阶段。施氮对两种群落多年生功能群的相对生物量无影响。因此，即使在低盐碱胁迫下，N添加也没有明显促进植物向多年生群落的演替。物种丰富度没有响应N除了在高应力的社会，而物种丰富度下降的N除了梯度在low-stress community.ConclusionOur结果提供了直接的经验证据，高盐碱胁迫限制植物群落演替，和低盐碱胁迫社区表现出的演替方向，从一年生为主的阶段，常年为主的阶段。有趣的是，在低胁迫条件下，相同处理的重复没有朝着相似的群落组成发展，这表明在小的空间尺度上环境异质性的重要性。氮添加并没有促进预期的多年生植物演替;然而，氮富集降低了植物多样性，提高了地上生物量，这表明人工氮添加（例如氮沉降）可能在我们的系统中产生重要影响。
Question(1) How do secondary successional dynamics differ in high and low saline‐alkaline grassland communities in semi‐arid lands; and (2) does nitrogen (N) enrichment promote plant secondary succession towards a perennial community under saline‐alkaline stress?LocationSaline‐alkaline grassland in northeast China.MethodsWe selected two early successional communities differing in soil saline‐alkaline stress and floristic composition: one ‘high‐stress community’ co‐dominated by the annual grassChloris virgataand the annual forbsArtemisia scopariaandKochia sieversiana, and one ‘low‐stress community’ dominated by the annual forbK. sieversiana. A complete randomized design experiment with five N addition levels was conducted in triplicate for four consecutive years (2008–2011). The vegetation variables (above‐ground biomass of individual species, functional group, community level, community species richness) and soil characteristics (pH, electrical conductivity as a proxy for salinity) were investigated every year. Detrended correspondence analysis (DCA) was used to evaluate the successional trajectories.ResultsDCA revealed clear differences in species composition and successional trajectories between the two communities. There were few changes in the species composition of the high‐stress community, with annual species dominating all the plots over the 4 yr. However, most of the low‐stress communities developed from the annual‐dominated stage to the perennial‐dominated stage. N addition had no effect on the relative biomass of the perennial functional group in the two communities. Thus, N addition did not obviously promote plant succession towards a perennial community, even under low saline‐alkaline stress. Species richness did not respond to N addition in the high‐stress community, whereas species richness declined across the N addition gradient in the low‐stress community.ConclusionOur results provided direct empirical evidence that high saline‐alkaline stress limits plant community succession, and low saline‐alkaline stress communities exhibit a succession direction from the annual‐dominated stage to the perennial‐dominated stage. Interestingly, replicates within the same treatment under low‐stress conditions did not develop towards a similar community composition, indicating the importance of environment heterogeneity at a small spatial scale. N addition did not promote the expected perennial plant succession; however, N enrichment reduced plant diversity and enhanced above‐ground biomass, suggesting that artificial N addition (e.g. N deposition) may have an important effect in our system.