FUTURE WORK
Including regional variations in soil invertebrate effects on
biogeochemistry to conceptual and predicting models. The temperate bias
of studies examining the role of invertebrates in decomposition means
that much of the raw data for existing biogeochemical models are from
non-tropical zones, which may result in an underestimation of soil
invertebrate effects on carbon flux and nutrient turnover. Moreover,
invertebrate biodiversity has been under tremendous pressure, with
knock-on effects on soil health, plant growth and climate regulation.
The tropics represent 36% of earth’s landmass and support the majority
of aboveground plant biomass
(Crowther et al. 2019). The regional differences in invertebrate
functions we have reported suggests that the loss of invertebrate
biodiversity could be particularly catastrophic in the Tropics.
More empirical studies needed in Africa and Australia. As with many
meta-analyses in ecology, only a small number of studies have occurred
in Australia and Africa, where large areas of tropical dry forests and
rainforests are located (Pan et al. 2013). We have repeatedly
stressed the relative importance of the termites in driving tropical
decomposition. Termites are diverse in both Australia and Africa.
Africa, indeed, is the evolutionary cradle of termites and hosts the
highest number of termite species (Buitenwerf et al. 2011;
Bignell 2019). The lack of observations in these areas suggests that we
may have underestimated tropical invertebrate effects on forest litter
decomposition. We urge, extensive data collection in the tropics,
especially in Africa, as essential for future assessments of global
carbon cycling and nutrient turnover.
Detailed information on litter traits and environmental variables are
needed. We suggest that detailed measurements of leaf litter traits need
to be included in further studies of litter decomposition. We advocate
for the establishment of a global dataset of leaf litter traits. No such
comprehensive global dataset for leaf litter traits exists. Contrasts
with living leaves (for which global data bases do exist (Kattgeet al. 2020)) will be informative. In addition, information on
plant communities, plot-based microclimates and soil properties should
accompany future studies since they are important factors driving the
ecological functions of soil invertebrate. Collecting such data at a
local scales is essential (Bradford et al. 2014).
Protocol used to exclude soil invertebrates. To date, most studies have
used physical methods (i.e. litterbags and mesocosms) to exclude soil
invertebrates in field experiments, accounting for 85% of observations
in our meta-data. Sixteen percent of observations in our meta-data
showed negative effects of invertebrates on litter mass loss. These
negative faunal effects on decomposition have not been well tested.
Possible explanations would be non-target effects of chemicals (e.g.
naphthalene) on both invertebrates and microbes (Lan et al.2020). Within the observations of negative faunal effects in our
meta-data, 62% of observations were from the use of naphthalene to
exclude invertebrates. The inclusion of fungivores such as Collembola
and Nematoda may affect microbial decomposition negatively (Johnsonet al. 2005) in cold or dry regions where invertebrate activity
is constrained by temperature and water availability (Wall et al.2008). Our analysis shows an insignificant relationship between
exclusion method and invertebrate effects on forest litter
decomposition. The potential non-target effects of chemicals such as
naphthalene on soil organisms and environments
(Lan et al. 2020),
however, leads us to advocate use of physical exclusion methods (Lanet al. 2019), particularly in highly stochastic tropical
rainforests and in regions with high
precipitation.