Inferring community assembly mechanisms from functional and phylogenetic diversity: The relative contribution of environmental filtering decreases along a sand desertification gradient in a desert steppe community

Abstract

The stress‐dominance hypothesis (SDH) predicts that environmental filtering will dominate in harsh habitats, while limiting similarity is more important in favourable environments. Here, we test the generality of the SDH to disentangle the relative importance of these two ecological processes along a sand desertification gradient. Data were collected from randomly selected locations in a desert steppe community in Northwest China. In this region, intense habitat fragmentation has resulted in a series of original soil habitat patches called soil islands. These soil islands typically contain Sierozem soils historically subjected to low (L), medium (M), and high (H) levels of sand desertification. Along this sand desertification gradient, soil properties and leaf traits (LDMC, leaf dry matter content; SLA, specific leaf area; LC, leaf carbon concentration; LP, leaf phosphorus concentration; and LN, leaf nitrogen concentration) were measured. We then tested for trait and phylogenetic convergence or divergence using a null model approach. Along the sand desertification gradient, trait convergence trend decreased, while trait divergence trend increased. Similarly, the phylogenetic convergence trends decreased. Traits displaying convergence included LDMC, SLA, and LCC, while LP and LN displayed divergence. The strength of LDMC convergence was negatively correlated with community weighted mean trait values (CWM) for LDMC. In contrast, the strength of LN divergence was positively correlated with CWM for LN. Our results pertaining to LDMC and LN support the SDH. Along the sand desertification gradient, the strength of environmental filtering gradually decreased, while the intensity of limiting similarity gradually increased.

Testing the Functional and Phylogenetic Assembly of Plant Communities in Gobi Deserts of Northern Qinghai–Tibet Plateau

“…However, the weaker competitor hypothesis also believes that relatively weaker competitive species would be excluded by relatively higher competitive species and can result in trait convergence (Mayfield and Levine, 2010 ). Additionally, our results partly support the importance of competitive exclusion, that is, LNC and LPC showed functional divergence, which is similar to the findings on desert steppe (Wang et al, 2021b ). Overall, we highlight that multiple niche-based processes, such as abiotic filtering and weaker competitive exclusion, determine plant functional assembly.…”

“…A previous study reported that plant functional and phylogenetic convergence showed a trend decreased along the sand desertification gradient (Wang et al, 2021b ). The phylogenetic and functional structure of tree communities also showed similar shifts along a climatic gradient in Yulong Mountain (Luo et al, 2019 ).…”

“…Mean pairwise distances (MPD) of functional trait of all species within the community was used to determine the functional structure, and MPD was assessed for each of the six individual functional traits as well as for six of the traits combined. MPD is the mean functional and phylogenetic distance among all pairs of species within a community, which is widely used to infer community assembly structure in previous studies (Luo et al, 2020 ; Wang et al, 2021b ). Meanwhile, the phylogenetic structure was determined as the MPD of species' phylogenetic relatedness.…”

“…Therefore, testing the relative roles of the different processes in shaping plant functional and phylogenetic structure in the Gobi deserts of TP may provide new insights into the mechanisms underlying the generation and maintenance of plant diversity under global change. Indeed, the plant community assembly and its determinants have been well examined in steppe and meadow ecosystems of TP (Wang et al, 2021a , b ). However, few studies to date have focused on elucidating the assembly processes that determine plant functional and phylogenetic structures across the Gobi deserts of TP.…”

Divergent Abiotic Stressors Drive Grassland Community Assembly of Tibet and Mongolia Plateau

“…This indicates that trait-convergence processes, such as abiotic filtering or weaker competitive exclusion, govern grassland community assembly ( Grime, 2006 ; Mayfield and Levine, 2010 ; Backhaus et al, 2021 ). Previous studies on forests have reported the prevalence of trait divergence in tree assemblages ( Luo et al, 2019 , 2021 ), while study on desert steppe observed a convergent trait frequency distribution ( Wang X. et al, 2021 ). The interpretation for those discrepancy between forest and grassland might be that, harsh grassland environment leads to a stronger abiotic filtering or weaker competitive exclusion, which reduce the range of trait values (convergence; De Bello et al, 2009 ; Kraft and Ackerly, 2010 ), while limiting similarity dominates in weaker stressful forest, thereby results in a high trait diversity (divergence; Mayfield and Levine, 2010 ).…”