Long‐term C, N and P allocation to reproduction in Bornean tropical rain forests

Abstract

Summary1. Tropical rain forests in SE Asia are well known for the occurrence of supra-annual synchronous reproductive events, masting. Answering the question how trees allocate carbon (C), nitrogen (N) and phosphorus (P) to such irregular but gregarious reproduction requires a long-term observation. We conducted a 10-year continuous monitoring of litterfall in eight tropical rain forests, which differ significantly in P (and N) availability on Mount Kinabalu, Borneo. 2. Mean P concentration in reproductive organ litter decreased significantly with increasing P-use efficiency of net primary production (PUE), an index of P deficiency. Therefore, P in reproductive organ litter became diluted as the magnitude of P deficiency increased. Mean annual litterfall (kg haÀ1 yr À1 ) of reproductive organs over the 10 years ranged from 128.5 to 730.9 across the eight forests. Long-term C allocation ratio to reproductive organs (i.e. C in reproductive organs per C in total litterfall) varied from 2.0% to 7.8% across the eight forests and did not relate with PUE, indicating that long-term C allocation ratio to reproduction was not controlled by the availability of the most critical soil nutrient. 4. Long-term N allocation ratio to reproduction varied from 2.7% to 9.9% and significantly positively related with C allocation ratio. The quotient of N allocation ratio to C allocation ratio ranged from 1.1 to 1.4. Long-term P allocation ratio to reproduction varied from 9.8% to 16.4%. The quotient of P allocation ratio to C allocation ratio ranged from 1.6 to 5.0. Therefore, tropical trees allocated much greater proportion of P to reproduction than C and N over the 10 years. Moreover, trees disproportionately increased P allocation to reproduction with decreasing C allocation to reproduction. Trees adjusted P allocation relative to C allocation and maintained a narrow range of P allocation ratio to reproduction in the long run in each site. 5. Synthesis. Reproduction in Bornean tropical rain forests costs more P than C and N. Our results suggest that reproductive events in these forests are regulated by P at the level of overall long-term mean. Understanding patterns and processes of reproductive events requires a long-term monitoring of nutrient dynamics.

Abrupt increase in phosphorus and potassium fluxes during a masting event in a Bornean tropical forest

“…Phosphorus (P) most frequently regulates tropical forest productivity (Vitousek 1984;Kitayama and Aiba 2002), suggesting that P may also limit tropical forest reproduction (see below for definition of the nutrient limitation to reproduction). In line with this hypothesis, Kitayama et al (2015) demonstrated a longterm trend in nine Bornean tropical rainforests for allocation of a disproportionately higher amount of P than C and N to reproduction; approximately 17% of P was allocated to reproduction, whereas C and N allocation was less than 10%. This finding indicated the significance of P for reproduction in Bornean tropical rainforests.…”

“…We calculated nutrient-use efficiency of above-ground net primary production by dividing the total litterfall flux by the total nutrient flux (E). Nutrient-use efficiency can be considered an index of realized P deficiency (Vitousek 1984; Kitayama et al 2015). We compared the nutrient-use efficiency and E at the present study site with data for other tropical regions to understand the characteristics of the present study site, and how the masting event affected nutrient flux and ecosystem productivity.…”

“…The best-fitting model included no explanatory variables, both for leaf and twig production (see the main text for the analysis details) Tables S3 and S4 (for woody stems and coarse roots, respectively) ( Fig. 2) (see also Kitayama et al 2015), and (2) trees species may have a lower capacity to store N than other elements (see the explanation below), and therefore do not rely on stored N for reproduction. Plants generally store N as organic amino acids or proteins, whereas the other rock-derived nutrients (e.g., P and K) are stored as inorganic forms (Chapin et al 1990).…”

Influence of temperature and soil nitrogen and phosphorus availabilities on fine‐root productivity in tropical rainforests on Mount Kinabalu, Borneo

“…The above-ground NPP (ANPP) was calculated as the sum of the above-ground biomass increment and the above-ground litterfall ( Table 1). The above-ground litterfall at each site was derived from the mean value of the 10-year observations between 1996 and 2006, as reported in Kitayama et al (2015).…”

Plant–soil interactions maintain biodiversity and functions of tropical forest ecosystems

“…This nutrient demand reaches the same order of magnitude of annual N and P demand for annual litter production [3.0-3.7 kg P ha À1 year À1 from Fujii et al (2011) and Kitayama et al (2015)]. Phosphorus availability could therefore limit annual fruit production in dipterocarp forests in Southeast Asia.…”