生態(tài)學(xué)的一個(gè)主要挑戰(zhàn)是理解不同物種如何相互作用來(lái)決定生態(tài)系統(tǒng)功能，特別是在具有大量共存物種的群落中。本研究使用基于性狀的微生物凋落物分解模型來(lái)量化不同類群對(duì)生態(tài)系統(tǒng)功能的影響。此外，本研究構(gòu)建了一個(gè)新穎的框架，使用DEMENT模擬器在環(huán)境、潮濕和干旱的氣候情景下進(jìn)行了微生物排除實(shí)驗(yàn)，突出了分類群特征和環(huán)境條件之間的相互作用，重點(diǎn)關(guān)注它們對(duì)群落相互作用和生態(tài)系統(tǒng)功能的綜合影響。結(jié)果表明，一個(gè)類群的生態(tài)系統(tǒng)影響是由其資源獲取特征和群落功能能力驅(qū)動(dòng)的，但生理脅迫放大了正負(fù)相互作用的影響。此外，即使微生物與其他類群之間存在負(fù)的兩兩相互作用，也可能對(duì)生態(tài)系統(tǒng)功能產(chǎn)生凈的積極影響。隨著群落對(duì)全球氣候變化響應(yīng)的轉(zhuǎn)變，本研究結(jié)果揭示了從分類群特征和相互作用預(yù)測(cè)群落生物地球化學(xué)功能的潛力。
FIGURE 1|Schematic of the DEMENT model and experimental design.(A)DEMENT is spatially explicit and represents microbial traits,taxon dynamics,community interactions and emergent functioning.(B)We modelled 10 substrates,50 enzymes,12 monomers(one for each substrate as well as two pools that represent inorganic nitrogen and phosphorus)and 25 microbial taxa.(C)To quantify taxon impacts on ecosystem function,we conducted exclusion experiments in which we removed a focal taxon from the initialization.The black line indicates a simulation with all taxa present.Grey lines indicate exclusion simulations without the focal taxon.
FIGURE 2|(A)Total substrate degradation varied significantly with both climate scenario(F251.88=17,712,p<0.05)and community context(F251.88=221.7,p<0.05).Total substrate degradation decreased with drought and increased with community-average enzyme production.Points are ordered on the x-axis and coloured by community-average enzyme production.(B)Taxon impacts on ecosystem function,defined as the change in substrate degradation when a focal taxon is excluded.(C)Taxon impacts on community dynamics,defined as the pairwise change in average biomass of an associate taxon when a focal taxon is excluded.
FIGURE 3|(A)The impact of a focal taxon on substrate degradation is positively related to the taxon-specific relative enzyme production,but the relationship is mediated by community-average relative enzyme production(Cenz)and climate.Points are coloured by climate scenarios.Data are shown here for representative communities with low and high Cenz,but analyses were conducted for all 50 replicate communities.The black lines represent the predicted taxon impact from a linear regression that includes taxon-specific relative enzyme production,community-average relative enzyme production,climate conditions and their interaction(p-value<0.001,R2=0.45).(B)The relationship between the impact of a focal taxon on substrate degradation and taxon-specific relative enzyme production(i.e.the slope from Panel A)is negatively related to community-average relative enzyme production and mediated by climate conditions(multiple regression:p-value<0.001,R2=0.70).
FIGURE 4|Taxon impacts on substrate degradation in relation to drought tolerance.Points are coloured by taxon-specific exo-enzyme production relative to monomer use,with lower values representing cheating strategies.Data are shown from simulations under the drought climate scenario.
FIGURE 5|(A)Focal taxon impacts on associate biomass and substrate degradation.Points are coloured by taxon-specific exo-enzyme production relative to monomer use,with lower values representing cheating strategies.(B)A generalisable framework for predicting taxon impacts on community dynamics and ecosystem function.Traits associated with resource acquisition determine whether impacts on ecosystem function will be positive or negative,but environmental stress amplifies the impact on ecosystem function in both positive and negative directions.In our simulations,under low environmental stress,focal taxa did not have meaningful impacts on substrate degradation regardless of taxon traits.When environmental stress was high,taxa that invested in greater enzyme production had more positive impacts on resource degradation.Trait dissimilarity between the focal taxon and the associate taxa determines whether exclusion of the focal taxon will lead to positive or negative impacts on the associate's fitness(y-axis position).Analysis of our data showed that,when a focal taxon had high positive impacts on substrate degradation,similar taxa tended to have competitive interactions and dissimilar taxa tended to have facilitative interactions.Furthermore,there were very few focal taxa that had negative impacts on substrate degradation and positive impacts on associate taxa(upper left quadrant)because positive impacts on associates require higher rates of enzyme production by the focal taxon.
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