Links between plant and fungal diversity in habitat fragments of coastal shrubland

Habitat fragmentation is widespread across ecosystems, detrimentally affecting biodiversity. Although most habitat fragmentation studies have been conducted on macroscopic organisms, microbial communities and fungal processes may also be threatened by fragmentation. This study investigated whether fragmentation, and the effects of fragmentation on plants, altered fungal diversity and function within a fragmented shrubland in southern California. Using fluorimetric techniques, we assayed enzymes from plant litter collected from fragments of varying sizes to investigate enzymatic responses to fragmentation. To isolate the effects of plant richness from those of fragment size on fungi, we deployed litter bags containing different levels of plant litter diversity into the largest fragment and incubated in the field for one year. Following field incubation, we determined litter mass loss and conducted molecular analyses of fungal communities. We found that leaf-litter enzyme activity declined in smaller habitat fragments with less diverse vegetation. Moreover, we detected greater litter mass loss in litter bags containing more diverse plant litter. Additionally, bags with greater plant litter diversity harbored greater numbers of fungal taxa. These findings suggest that both plant litter resources and fungal function may be affected by habitat fragmentation's constraints on plants, possibly because plant species differ chemically, and may thus decompose at different rates. Diverse plant assemblages may produce a greater variety of litter resources and provide more ecological niche space, which may support greater numbers of fungal taxa. Thus, reduced plant diversity may constrain both fungal taxa richness and decomposition in fragmented coastal shrublands. Altogether, our findings provide evidence that even fungi may be affected by human-driven habitat fragmentation via direct effects of fragmentation on plants. Our findings underscore the importance of restoring diverse vegetation communities within larger coastal sage scrub fragments and suggest that this may be an effective way to improve the functional capacity of degraded sites.

生境破碎化（habitat fragmentation）在各类生态系统中广泛分布，会对生物多样性造成不利影响。尽管当前多数生境破碎化相关研究均以大型生物为对象，但微生物群落与真菌过程同样可能受到破碎化的威胁。本研究针对加利福尼亚南部一处破碎化灌丛生态系统展开调查，旨在探究破碎化及其对植物的影响是否会改变真菌多样性与功能。本研究采用荧光测定技术（fluorimetric techniques），对从不同面积的破碎化生境中采集的植物凋落物进行酶活性检测，以探究酶促反应对破碎化的响应。为区分植物丰富度与生境斑块面积对真菌的影响，我们将搭载不同植物凋落物多样性梯度的凋落袋（litter bags）置入最大的破碎化斑块中，并开展为期一年的野外培养实验。野外培养结束后，我们测定了凋落物的质量损失率，并对真菌群落进行了分子生物学分析。研究结果显示，植被多样性更低的小型生境破碎化斑块中，叶片凋落物的酶活性显著下降。此外，搭载植物凋落物多样性更高的凋落袋中，凋落物质量损失率显著更高。同时，植物凋落物多样性更高的凋落袋内，真菌类群的丰度也显著更高。上述结果表明，生境破碎化通过作用于植物进而影响植物凋落物资源与真菌功能，其潜在机制可能是不同植物物种的化学组成存在差异，从而导致分解速率各不相同。多样的植物群落可产生更为丰富的凋落物资源，并提供更多的生态位空间，从而维持更高丰度的真菌类群。因此，植物多样性的降低可能会限制沿海破碎化灌丛生态系统中的真菌类群丰富度与分解过程。综上，本研究结果证实，即使是真菌也可能通过破碎化对植物的直接作用，受到人类活动驱动的生境破碎化的影响。本研究结果强调了在更大面积的沿海鼠尾草灌丛破碎化斑块中恢复多样植物群落的重要性，并指出这或许是提升受损生境功能能力的有效途径。