Cycling and retention of nitrogen in European beech (<i>Fagus sylvatica</i> L.) ecosystems under elevated fructification frequency

Abstract

Abstract. Atmospheric deposition of nitrogen (N) has exceeded its demand for plant increment in forest ecosystems in Germany. High N inputs increased plant growth, the internal N cycling within the ecosystem, the retention of N in soil and plant compartments, and the N output by seepage water. But the processes involved are not fully understood, notably the effect of fructification in European beech (Fagus sylvatica L.) on N fluxes. The frequency of fructification has increased together with air temperature and N deposition, but its impact on N fluxes and the sequestration of carbon (C) and N in soils have been hardly studied. A field experiment using 15N-labeled leaf litter exchange was carried out over a 5.5-year period at seven long-term European beech (Fagus sylvatica L.) monitoring sites to study the impact of current mast frequency on N cycling. Mean annual leaf litterfall contained 35 kg N ha−1, but about one-half of that was recovered in the soil 5.5 years after the establishment of the leaf litter 15N exchange experiment. In these forests, fructification occurred commonly at intervals of 5 to 10 years, which has now changed to every 2 years as observed during this study period. Seed cupules contributed 51 % to the additional litterfall in mast years, which creates a high nutrient demand during their decomposition due to the very high ratios of C to N and C to phosphorus (P). Retention of leaf litter 15N in the soil was more closely related to the production of total litterfall than to the leaf litterfall, indicating the role of seed cupules in the amount of leaf N retained in the soil. Higher mast frequency increased the mass of mean annual litterfall by about 0.5 Mg ha−1 and of litterfall N by 8.7 kg ha−1. Mean net primary production (NPP) increased by about 4 %. Mean total N retention in soils calculated by input and output fluxes was unrelated to total litterfall, indicating that mast events were not the primary factor controlling total N retention in soils. Despite reduced N deposition since the 1990s, about 5.7 out of 20.7 kg N ha−1 deposited annually between 1994 and 2008 was retained in soils, notably at acid sites with high N/P and C/P ratios in the organic layers and mineral soils, indicating P limitation for litter decomposition. Trees retained twice as much N compared to soils by biomass increment, particularly in less acidic stands where the mineral soils had low C/N ratios. These results have major implications for our understanding of the C and N cycling and N retention in forest ecosystems. In particular the role of mast products in N retention needs more research in the future.

Costs and benefits of masting: economies of scale are not reduced by negative density‐dependence in seedling survival in Sorbus aucuparia

“…Synchronous and highly variable seed production among years by populations of perennial plants, or masting, is widespread reproductive strategy in the plant kingdom (Kelly & Sork, 2002; Dale et al ., 2021). The variable seed production is implicated in many ecological processes, from macronutrient cycles to resource pulses that have cascading effects on plant and animal population dynamics (Ostfeld & Keesing, 2000; Bogdziewicz et al ., 2016; Clark et al ., 2019; Brumme et al ., 2021). Masting is hypothesized to result from selection that promotes variability and synchrony through economies of scale, mainly increased pollination efficiency in years of extensive flowering, and satiation of seed predators in years of bumper crops (Norton & Kelly, 1988; Pearse et al ., 2016; Bogdziewicz et al ., 2020a).…”

MASTREE+: Time‐series of plant reproductive effort from six continents

“…In masting species, highly variable allocation to reproduction has wider effects on plant resource allocation, and carbon and nutrient cycling through ecosystems, but this remains poorly explored (Brumme et al, 2021; Khanna et al, 2009; Muller‐Haubold et al, 2015). Data in MASTREE+ can be combined with existing field and remote‐sensing data sets of plant growth or productivity, and with data sets of whole‐ecosystem or soil carbon and nutrient fluxes to understand how variable allocation to reproduction influences carbon sequestration above and belowground, and how this varies between species and across environmental gradients (Bajocco et al, 2021; Nussbaumer et al, 2021; Oddou‐Muratorio et al, 2021; Zhang et al, 2022).…”

“…In masting species, highly variable allocation to reproduction has wider effects on plant resource allocation, and carbon and nutrient cycling through ecosystems, but this remains poorly explored (Brumme et al, 2021;Khanna et al, 2009;Muller-Haubold et al, 2015). Data in MASTREE+ can be combined with existing field and remote-sensing data sets of plant growth or productivity, and with data sets of whole-ecosystem or soil carbon and nutrient fluxes to existing or retrospective sampling (e.g.…”

“…MASTREE+ provides these time‐series of plant reproductive effort, and will enable testing of changes in masting patterns associated with recent environmental change across multiple species and geographical regions (Hacket‐Pain & Bogdziewicz, 2021; LaMontagne et al, 2021; Pearse et al, 2017). Such data sets will also enable new insights into the ecology and evolution of perennial plant reproduction (Dale et al, 2021), and the role of plant reproduction as a driver of other ecological processes including plant recruitment and animal population dynamics (Brumme et al, 2021; Connell & Green, 2000; Curran & Leighton, 2000; Schupp et al, 2019).…”

Supplementary material to "Reviews and syntheses: VOC emissions from soil cover in boreal and temperate natural ecosystems of the Northern Hemisphere "

“…In the literature, one can find only a few reports on this topic, some information of which is presented in Table S2. Analysis of works published in recent years shows that litter is measured in the framework of research on specific sites (Gomez-Armesto et al, 2020;Petritan et al, 2020;Jasińska et al, 2020;Brumme et al, 2021;Ott and Watmough, 2021). For a number of those studies cited in Table S3, the refinement of litter biomass is a subordinate task that allows to obtain, when recalculated, data on the mass of chemical elements, for example, C, N, P, Hg, etc., to describe their accumulation in litter and to establish the quantitative series of chemical elements and their ratio (C/N) (Jasi'nska et al, 2020).…”