sequestration and SOM are important to the maintenance of the equilibrium of C/N
in soils, thus benefiting microbial activity and ensuring enough enzymes for
nutrient cycling. Indeed, climate warming affects soil carbon (C) dynamics, with
possible serious consequences for soil C stocks and atmospheric CO 2 concentrations but, the mechanisms underlying changes in soil C storage are not well
understood, hampering long-term predictions of climate C-feedbacks [82].
A meta-analysis has shown that reductions in soil C stocks with warming are
associated with increased ratios of ligninase to cellulase activity that can be used to
track changes in the predominant C sources of soil microbes and can thus provide
mechanistic insights into soil C loss pathways. Results suggest that warming
stimulates microbial utilization of recalcitrant C pools, possibly exacerbating
long-term climate-C feedbacks [82].
A long-term field manipulation experiment has provided evidence that soil
aggregate size independently mediates soil microbial feedbacks to multiple climate
change factors [83]. Altered microbial enzyme activities, enzyme stoichiometry,
and specific enzyme activities under climate change were mainly consistent across
soil aggregate size classes. An exception was that C degrading enzyme activities
were greatest where C concentrations were highest, namely in the micro-aggregates.
Moreover, climate change increased specific enzyme activities for C decomposition, suggesting positive feedbacks between microbial activities related to SOM
decomposition and climate change. The distribution of aggregates within soils is
affected by both physical and biological processes, and therefore not only affects
microbial function but is also affected by it. Previous studies have found that soil
aggregate size exerted strong impacts on soil C dynamics and microbial activity.
For example, a study of microbial community profiles and activities among
aggregates of winter fallow and cover-cropped soil has shown that microorganisms
and their activities can be heterogeneously distributed among soil aggregates, and
their distribution may change in response to management practices that affect
aggregate [84]. Lack of community differentiation may be due to the frequent
mixing of soil during cultivation and tillage events, whereby microbial communities
become evenly distributed among soil aggregates.
Gong et al. [85] show the response of soil enzyme activity to warming and
nitrogen addition in a meadow steppe. Soil enzyme activity, soil microclimate and
soil nutrients were measured to investigate the response of soil enzyme activity to N
addition and experimental warming. Warming enhanced phosphatase activity
(35.8%) but inhibited the cellulase activity (30%). Nitrogen addition significantly
enhanced the activities of urease (34.5%) and phosphatase (33.5%) but had no
effect on cellulase activity. Significant interactive effects of warming and N addition
on soil enzyme activity were observed. In addition, warming reduced soil C (7.2%)
and available P (20.5%), whereas N addition increased soil total N (17.3%) and
available N (19.8%) but reduced soil C (7.3%), total P (14.9%) and available P
(23.5%). Cellulase and phosphatase activity was highly correlated with soil temperature and water content, whereas urease activity was determined primarily by
soil N availability. It is difficult to generalize the effects of warming on enzyme
pools, as they are also affected and affect other abiotic factors such as the above
148
C. M. d. S. Cordovil et al.
in soils, thus benefiting microbial activity and ensuring enough enzymes for
nutrient cycling. Indeed, climate warming affects soil carbon (C) dynamics, with
possible serious consequences for soil C stocks and atmospheric CO 2 concentrations but, the mechanisms underlying changes in soil C storage are not well
understood, hampering long-term predictions of climate C-feedbacks [82].
A meta-analysis has shown that reductions in soil C stocks with warming are
associated with increased ratios of ligninase to cellulase activity that can be used to
track changes in the predominant C sources of soil microbes and can thus provide
mechanistic insights into soil C loss pathways. Results suggest that warming
stimulates microbial utilization of recalcitrant C pools, possibly exacerbating
long-term climate-C feedbacks [82].
A long-term field manipulation experiment has provided evidence that soil
aggregate size independently mediates soil microbial feedbacks to multiple climate
change factors [83]. Altered microbial enzyme activities, enzyme stoichiometry,
and specific enzyme activities under climate change were mainly consistent across
soil aggregate size classes. An exception was that C degrading enzyme activities
were greatest where C concentrations were highest, namely in the micro-aggregates.
Moreover, climate change increased specific enzyme activities for C decomposition, suggesting positive feedbacks between microbial activities related to SOM
decomposition and climate change. The distribution of aggregates within soils is
affected by both physical and biological processes, and therefore not only affects
microbial function but is also affected by it. Previous studies have found that soil
aggregate size exerted strong impacts on soil C dynamics and microbial activity.
For example, a study of microbial community profiles and activities among
aggregates of winter fallow and cover-cropped soil has shown that microorganisms
and their activities can be heterogeneously distributed among soil aggregates, and
their distribution may change in response to management practices that affect
aggregate [84]. Lack of community differentiation may be due to the frequent
mixing of soil during cultivation and tillage events, whereby microbial communities
become evenly distributed among soil aggregates.
Gong et al. [85] show the response of soil enzyme activity to warming and
nitrogen addition in a meadow steppe. Soil enzyme activity, soil microclimate and
soil nutrients were measured to investigate the response of soil enzyme activity to N
addition and experimental warming. Warming enhanced phosphatase activity
(35.8%) but inhibited the cellulase activity (30%). Nitrogen addition significantly
enhanced the activities of urease (34.5%) and phosphatase (33.5%) but had no
effect on cellulase activity. Significant interactive effects of warming and N addition
on soil enzyme activity were observed. In addition, warming reduced soil C (7.2%)
and available P (20.5%), whereas N addition increased soil total N (17.3%) and
available N (19.8%) but reduced soil C (7.3%), total P (14.9%) and available P
(23.5%). Cellulase and phosphatase activity was highly correlated with soil temperature and water content, whereas urease activity was determined primarily by
soil N availability. It is difficult to generalize the effects of warming on enzyme
pools, as they are also affected and affect other abiotic factors such as the above
148
C. M. d. S. Cordovil et al.