Elevation, soil pH, and calcium availability shape regional and local scale spatial patterns of PhoD gene abundance in tropical and subtropical forests

Organic phosphorus mineralization is a critical process in the phosphorus
cycle, governing phosphorus bioavailability for plants. The PhoD gene,
which encodes the key enzyme alkaline phosphatase, serves as a valuable
biomarker for this process. Soil microbes harboring the PhoD gene mediate
this process by secreting extracellular alkaline phosphatases. This gene
is widespread across diverse bacterial phyla, and its significance has
been extensively reported in agroecosystems, particularly in response to
fertilizer inputs. However, the spatial distribution of the PhoD gene in
natural ecosystems along environmental gradients and its consequent
effects on phosphorus dynamics remain unclear. We investigated the spatial
distribution of the PhoD gene abundance across 20-ha study areas in
tropical (Nabanhe, Bubeng) and subtropical (Ailaoshan) forests spanning
broad elevation gradients but narrow latitudinal ranges. Our objectives
were to: (a) characterize its spatial patterns, (b) identify the key
drivers of its variation across local and regional scales, and (c)
determine the influence of soil chemical properties. PhoD gene abundance
and detectability differed sharply among forests. Abundance was highest
and most ubiquitous in mid-elevation Nabanhe (1015.86-1235.64 m),
intermediate in low-elevation Bubeng (712.05-860.05 m), and lowest in
high-elevation Ailaoshan (2443.78-2586.13 m), where the gene was
frequently undetectable. The most striking contrast was the high
prevalence of non-detection in Ailaoshan compared to the other sites. The
results identified elevation, soil pH, and calcium as the top three
predictors of PhoD gene abundance and distribution at the regional scale.
Soil pH was a consistent driver at both regional and local scales.
Regionally, the effect of elevation was mediated by changes in soil pH and
macronutrients (TC, TN, TP). However, at local scales, the spatial pattern
was associated with variations in soil parent material, which influenced
both soil pH and calcium. In summary, PhoD gene abundance varied
significantly across the forest ecosystems. Our investigation demonstrates
how elevation-driven environmental changes shape the genetic potential for
phosphorus mineralization, underscoring the need for broader-scale studies
to project the responses of this key microbial process to global change.