Ratios of phosphatase activity to activities of carbon and nitrogen-acquiring enzymes in throughfall were larger in tropical forests than a temperate forest

Abstract

Tropical forests are considered as phosphorus (P)-poor ecosystems, where microorganisms are suggested to allocate more resources to P acquisition compared to carbon (C) and/or nitrogen (N) acquisition. Therefore, ratios of activities of acid/alkaline phosphomonoesterase (AP) to C-acquiring enzymes such as β-1,4-glucosidase (BG) and C and/or N-acquiring enzymes such as β-1,4-N-acetyl-glucosaminidase (NAG) and leucine amino peptidase (LAP) are generally larger in tropical forest soils (i.e., BG: AP and (NAG+LAP): AP are smaller). However, those ratios were never reported for enzymes in throughfall. In this short note, we reported that both BG: AP and (NAG+LAP): AP of throughfall samples were smaller in five tropical forests than those in a temperate forest, which was consistent with generally-observed patterns in soils. This implies that phyllosphere microorganisms may allocate more resources to obtain P in P-poor tropical forest canopy, which should be considered in future P cycling quantifications in forest ecosystems.

Importance of Considering Enzyme Degradation for Interpreting the Response of Soil Enzyme Activity to Nutrient Addition: Insights from a Field and Laboratory Study

“…Litters deposited on the forest floor provide nutrients to the soil, but it is the enzymes that break down the organic matter, allowing organisms to reuse the nutrients. Soil extracellular enzymes are predominantly synthesized by soil microorganisms and plant roots, but leaf litter [5] or throughfall [6][7][8] can also contribute to the pool of soil extracellular enzymes. In ecosystems where multiple enzymes coexist, the activity of soil extracellular enzymes (i.e., V max ) can serve as an indicator of enzyme abundance [9,10].…”

“…In field conditions, plants continuously supply resources such as C and nutrients through litters and root exudates. Additionally, plants also provide enzymes to soils through litter layers [5] or throughfall [6,8]. However, the degree to which these resources or enzyme supplies contribute to the soil enzyme pool remains unknown.…”

Effects of phosphorus addition on leaf litter decomposition in two tropical tree plantations in Thailand

“…A nutrient that limits an ecological process (such as net primary production) can be defined as follows: a nutrient is limiting when the potential rate of an ecological process (such as net primary production), allowing for possible shifts in the species composition, is suppressed by a lack of the nutrient (modified from the definitions by Gibson 1971 andHowarth 1988, see Mori et al 2018). Tropical forests are known to be a phosphorus (P)-poor ecosystem (Vitousek 1984;Kitayama and Aiba 2002;Cleveland et al 2002;Mori et al 2021), and thus ecosystem processes, such as primary production, in tropical forests are long considered to be limited by P availability (Walker and Syers 1976;Vitousek 1984;Crews et al 1995;Vitousek and Farrington 1997;Elser et al 2007). This is because soils are highly weathered and remaining P is occluded on aluminum and iron oxides which have a strong affinity for P (Miller et al 2001;Chapin et al 2002).…”