N-Induced Species Loss Dampened by Clipping Mainly Through Suppressing Dominant Species in an Alpine Meadow

Abstract

Nitrogen addition and clipping can exert substantial impact on species diversity but their interactions and the underlying mechanisms still remain unclear. Resource competition theory holds that sufficiently strong competitive ability of dominant species can lead to the losses of subordinate species through competitive exclusion, while niche differentiation theory suggests that the persistence of subordinate species in competitive systems can be promoted by guaranteeing positive growth rates of rare species. Taking advantage of a field experiment with nitrogen addition (10 g N m–2 year–1) and different clipping intensities (2, 15, and 30 cm) treatments in a Tibetan alpine meadow across 2015–2020, we assessed the relative importance of competitively dominant species and niche differentiation in driving species diversity changes via using community weighted mean (CWM) and variation coefficient of nearest neighbor distance (CV_NND) of functional traits including height, specific leaf area (SLA) and leaf dry matter content (LDMC). We show that nitrogen enrichment drove a strong plant diversity loss (P < 0.001). Clipping at different intensities had little effect on species diversity, but it can reduce the N-induced diversity loss. Nitrogen addition and clipping caused changes in community diversity were mainly indirectly attributed to their effects on community functional composition, and the competitive ability of dominant species. Nitrogen increased the CWM of functional traits to improve the competitive ability of dominant species. In contrast, clipping influenced species diversity positively by decreasing CWMheight (P < 0.001), and also negatively by increasing CWMSLA (P < 0.001) and decreasing CV_NNDSLA (P < 0.05). Interacting with N addition, clipping resulted in a neutral effect on species diversity, because clipping could offset the negative effects of nitrogen addition through an opposite effect on CWMheight. This study provides new insights into the mechanisms of diversity maintenance with respect to nitrogen addition and clipping. Thus, clipping is recommended as a useful management strategy to alleviate the species loss caused by nutrients enrichment and maintain the diversity of grassland ecosystems.

Response of soil bacteria on habitat-specialization and abundance gradient to different afforestation types

“…However, at the abundance gradient, the abundant subgroup owns a small number of OTUs species and a high abundance ratio, while the rare subgroup showed the opposite. Some studies also showed that the total number of sequences of abundant subgroup was dominant while the species number of rare subgroup was absolutely dominant 18 .…”

“…Then the zero distribution of the niche width index was calculated for each OTU. Based on the consensus that habitat-generalized subgroup owe a wider niche width than the habitat-specialized subgroup 40 , OTUs were classified into a habitat-generalized or a specialized group based on whether the frequency of observed occurrence exceeded the upper 95% confidence interval or fell below the lower 5% confidence interval, and the OTUs were distributed to the habitat-neutral group if the observed niche width was within in the 5% to 95% confidence interval range 18 . …”

“…Different vegetation types affect soil microbial diversity and community structure through altering the chemical composition and content of litter and root exudates, making them strongly related 15 , 16 . Vegetation types might also affect microbial community structure by regulating soil physicochemical properties 17 , in which soil pH, organic carbon could directly affect soil microbial community composition 18 . Soil pH, carbon nitrogen ratio, etc., have also been shown vital for soil microbial community structures 19 , 20 .…”