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Human‐induced environmental change is occurring globally and alters ecosystem properties both directly, by changing abiotic conditions, and indirectly, by modifying community composition. The effects of changes in plant composition in determining ecosystem properties may be determined by the identity of the plants, their respective biomass in the community and also by the ability of remaining vegetation to compensate for their loss.We used the graminoid removal treatment from a long‐term (12 year) removal experiment to examine the role of graminoids in determining ecosystem properties and also the potential for biomass compensation by remaining species in a grassland in northern Canada. We conducted removals in both fertilized and non‐fertilized environments to examine context‐dependency of graminoid effects.There was full biomass compensation for graminoid removal by the remaining functional groups (i.e., total biomass was equal to no‐removal controls) after 5 years, and after 12 years fertilized plots showed overcompensation for removals.After 12 years of graminoid removals, most ecosystem properties were not affected by removals in either fertilization environment. Similarly, there were few effects on microbial biomass or function with plant removal or fertilization treatments.Comparison to earlier published responses in this experiment shows a strengthening of the responses of the plant community to graminoid removals over time while effects on ecosystem properties diminished. Full biomass compensation for removal of graminoids occurred after 5 years, and after 12 years of removals, fertilized plots had overcompensated for the loss of graminoids. In contrast, the shorter term (4 years) responses of soil available nutrients and soil moisture to removals have mainly disappeared after eight further years, likely because of the biomass compensation by the plant community.Synthesis. Comparing the effects of graminoid removals on ecosystem structure and function after 4, 7, and now 10 and 12 years of removals, we now argue that, after over a decade of graminoid removal, recovery of plant biomass is required for the maintenance of most ecosystem properties and not functional group identity, as we concluded earlier. This highlights the importance of maintaining field experiments in the long term, particularly in northern ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: The soil community is an often ignored part of research which links plant biodiversity and ecosystem functioning despite their influence on numerous functions such as decomposition and nutrient cycling. Few consistent patterns have been detected that link plant and soil community composition. We used a removal experiment in a northern Canadian grassland to examine the effects of plant functional group identity on soil microbial community structure and function. Plant functional groups (graminoids, legumes and forbs) were removed independently from plots for five growing seasons (2003–2007) and in the fifth year effects on the soil microbial community were examined using substrate-induced respiration (SIR – a measure of metabolic diversity) and phospholipid fatty acid analysis (PLFA – a measure of microbial community composition). Removal treatments were also crossed with both a fertilizer treatment and a fungicide treatment to determine if effects of functional group identity on the soil community were context dependent. Plant functional group identity had almost no effect on the soil microbial community as measured by either SIR or PLFA. Likewise, soil properties including total carbon, pH, moisture and nutrients showed a limited response to plant removals in the fifth year after removals. We found a direct effect of fertilizer on the soil community, with fertilized plots having decreased metabolic diversity, with a decreased ability to metabolize amino acids and a phenolic acid, but there was no direct soil microbial response to fungicide. We show that in this northern Canadian grassland the soil microbial community is relatively insensitive to changes in plant functional group composition, and suggest that in northern ecosystems, where plant material is only slowly incorporated into the soil, five growing seasons may be insufficient to detect the impact of a changing plant community on the soil microbes. [ABSTRACT FROM AUTHOR]

Global change in the Arctic promotes deeper soil thaw and enhanced soil microbial activity, increasing nitrogen (N) and phosphorus (P) availability to plants and microbes in strongly nutrient‐limited ecosystems. This critical, positive climate feedback has been examined through fertilization experiments that describe short‐term (<10 yr) above‐ or belowground responses to combined NP additions, with evidence of enhanced shrub growth, nutrient availability, and soil organic matter decomposition. There has been less opportunity for long‐term comparisons of both above‐ and belowground responses with factorial N and P additions in different systems, despite broad awareness that ecosystem response can shift with time, and the potential for decoupled above‐ vs. belowground or N vs. P responses, currently and with further predicted global change. We examined the response of the plants, soil microbes, and soil nutrients, to factorial N and P additions in the moist acidic tundra (MAT; 26 yr of nutrient additions) and moist non‐acidic tundra (MNT; 16 yr). Aboveground, the MAT plant community continues to change as predicted by earlier studies: Functional groups responded independently to N and P, but NDVI‐biomass, especially of Betula nana, only increased with N addition. Unlike shorter‐term MNT studies, the MNT vegetation, which does not include B. nana, shows few new fertilization responses. Belowground responses were not predicted by aboveground responses in either MAT or MNT. In contrast to the N response aboveground, MAT microbial biomass responded positively and microbial phosphatase activity negatively to P additions, implying possible release from microbial P limitation. Critically, earlier published results of declines in soil total carbon (C) with combined NP addition in the MAT are not present in the long term. We make two conclusions: (1) Arctic ecosystems are not universally N‐limited but also exhibit complex responses to P alone or in combination with N; and (2) the presence or absence of key vegetation species can cascade from aboveground to belowground and restrict the extrapolation of responses of nutrient addition in a single arctic ecosystem to other arctic ecosystems, the short‐term to the long term, or aboveground to belowground. [ABSTRACT FROM AUTHOR]