Reproductive response to nitrogen and phosphorus fertilization along the Hawaiian archipelago’s natural soil fertility gradient

Abstract

Nitrogen (N) and phosphorus (P) are the most important nutrients involved in plant reproduction and typically the most limiting in terrestrial ecosystems. The natural soil fertility gradient of the Hawaiian archipelago, in which younger islands are N limited and older islands are P limited, provides a model system to examine questions regarding allocation of nutrients. Using fertilized plots (+N or +P) at the extreme sites of the Hawaiian archipelago, vegetative productivity (e.g., net primary productivity, growth, and litterfall) and foliar nutrient responses have previously been studied for the dominant canopy tree, Metrosideros polymorpha. Here, we investigated whether the reproductive response of M. polymorpha mirrors the previously found vegetative productivity and foliar nutrient responses, by quantifying: (1) inflorescence and seed productivity, and (2) nutrient concentration of reproductive structures. Fertilization with N and P did not significantly affect the productivity of inflorescences or seeds, or seed viability at either site. However, nutrient concentrations increased after fertilization; %P increased in inflorescences in the +P treatment at the P-limited site. Seeds and inflorescences generally contained higher nutrient concentrations than leaves at both sites. Unlike foliar data, reproductive strategies of M. polymorpha differed depending on soil nutrient limitation with emphasis on quality (higher seed viability/greater nutrient concentrations) at the P-limited site. We suggest that in response to P additions M. polymorpha employs a nutrient conservation strategy for its inflorescences and an investment strategy for its seeds. Examining N and P simultaneously challenges a basic assumption that reproductive allocation follows a similar pattern to the often measured aboveground productivity.

A nurse plant benefits from facilitative interactions through mycorrhizae

“…As the quantity and quality of seeds are indicators of how the plant allocates resources according to nutrient availability in soil (Sinclair & Vadez ; Hulshof et al . ; Marschner ; DiManno & Ostertag ), our results strongly suggest that nurses living with their facilitated plants have greater access to resources via mycorrhiza. Similarly, fungicide could be negatively affecting the facilitated plants because the reduction of their extra‐radical mycelia decreases the volume of soil to explore and disrupts the connections with M. luisana through which N is received (Montesinos‐Navarro et al .…”

Relationships of phosphorus concentration in reproductive organs with soil phosphorus availability for tropical rain-forest trees on Mount Kinabalu, Borneo

“…This may be because tree species on P-poor soils accumulate P in seeds (DiManno & Ostertag 2016, Witkowski 1990). The accumulation of P in seeds was often found in species naturally growing on P-poor soils (Atkinson & Davison 1971, DiManno & Ostertag 2016, Groom & Lamont 2010, Witkowski 1990). For instance, DiManno & Ostertag (2016) conducted P or N fertilization experiments at two sites with contrasting soil fertility (P-limited sites vs. N-limited sites) in the Hawaiian Archipelago, and found that Metrosideros polymorpha (Myrtaceae) at the P-limited sites accumulated P in seeds in response to P fertilization while that at the N-limited sites did not.…”

“…Groom & Lamont (2010) showed that Proteaceae from south-western Australia (stronger P deficiency) had on average a two-fold greater P concentration in seeds than those from the Cape of Africa (weaker P deficiency). The accumulation of P in seeds is considered to be an adaptive mechanism to P deficiency (DiManno & Ostertag 2016, Lambers et al 2015), because the storage of P in seeds contributes to rapid seedling growth on P-poor soils (Groom & Lamont 2010, Thomson & Bolger 1993, Vandamme et al 2016). Exceptionally, P concentration in the seeds of Syzygium species significantly decreased with decreasing soil P availability.…”

“…6 out of 7 genera showed a positive sign in the Pearson's correlation coefficient of the OLS models, Appendix 2). This may be because tree species on P-poor soils accumulate P in seeds (DiManno & Ostertag 2016, Witkowski 1990). The accumulation of P in seeds was often found in species naturally growing on P-poor soils (Atkinson & Davison 1971, DiManno & Ostertag 2016, Groom & Lamont 2010, Witkowski 1990).…”

Seed-dispersal ecology of tropical montane forests

“…The contribution of each environmental characteristic to changes in plant traits, animal assemblages and microbial communities with increasing altitude (Figure 1) cannot easily be separated. However, the trend for smaller trees, lower diversity of fleshy-fruited tree species and smaller crop size can be directly linked to soil nutrient availability, especially nitrogen (N), which is critical for fruit production (DiManno & Ostertag 2016). Nitrogen often declines, or become less available to plants (Carbutt et al 2013) with increasing altitude, and this, together with fewer beneficial soil micro-organisms in TMF in general (Dalling et al 2016, Tanner et al 1998), leads to trade-offs in plant functional traits.…”