Peter M. Vitousek’s research while affiliated with Stanford University and other places

Advances in manufacturing and trade have reshaped global nitrogen deposition patterns, yet their dynamics and drivers remain unclear. Here, we compile a comprehensive global nitrogen deposition database spanning 1977–2021, aggregating 52,671 site-years of data from observation networks and published articles. This database show that global nitrogen deposition to land is 92.7 Tg N in 2020. Total nitrogen deposition increases initially, stabilizing after peaking in 2015. Developing countries at low and middle latitudes emerge as new hotspots. The gross domestic product per capita is found to be highly and non-linearly correlated with global nitrogen deposition dynamic evolution, and reduced nitrogen deposition peaks higher and earlier than oxidized nitrogen deposition. Our findings underscore the need for policies that align agricultural and industrial progress to facilitate the peak shift or reduction of nitrogen deposition in developing countries and to strengthen measures to address NH3 emission hotspots in developed countries.

Plant litter is a well-defined pool of organic matter (OM) in which the influence of manganese (Mn) on decomposition (both decomposition rate and the mix of compounds ultimately transferred to soil OM) has been clearly demonstrated in temperate forests. However, no similar study exists on grasslands and the effect of foliar Mn versus soil-derived Mn on litter decomposition is poorly known. We used a 5-month and 12-month field, and 10-month laboratory experiments to evaluate litter decomposition on the Kohala rainfall gradient (Island of Hawai‘i) in areas with different foliar and soil Mn abundances, and on which a single plant species (Pennisetum clandestinum) dominates primary production and the litter pool. The chemical imaging analyses of decomposed litter revealed that Mn²⁺ oxidized to Mn³⁺ and Mn⁴⁺ on grass litter during decompositions—hallmarks of Mn-driven litter oxidation. However, these transformations and Mn abundance did not predict greater litter mass loss through decomposition. These observations demonstrate that the importance of Mn to an ecosystem’s C cycle does not rely solely on the metal’s abundance and availability.

A recent publication (Mason et al. in Science 376:261, 2022a) suggested that nitrogen (N) availability has declined as a consequence of multiple ongoing components of anthropogenic global change. This suggestion is controversial, because human alteration of the global N cycle is substantial and has driven much-increased fixation of N globally. We used a simple model that has been validated across a climate gradient in Hawai ‘i to test the possibility of a widespread decline in N availability, the evidence supporting it, and the possible mechanisms underlying it. This analysis showed that a decrease in δ¹⁵N is not sufficient evidence for a decline in N availability, because δ¹⁵N in ecosystems reflects both the isotope ratios in inputs of N to the ecosystem AND fractionation of N isotopes as N cycles, with enrichment of the residual N in the ecosystem caused by greater losses of N by the fractionating pathways that are more important in N-rich sites. However, there is other evidence for declining N availability that is independent of ¹⁵N and that suggests a widespread decline in N availability. We evaluated whether and how components of anthropogenic global change could cause declining N availability. Earlier work had demonstrated that both increases in the variability of precipitation due to climate change and ecosystem-level disturbance could drive uncontrollable losses of N that reduce N availability and could cause persistent N limitation at equilibrium. Here we modelled climate-change-driven increases in temperature and increasing atmospheric concentrations of CO2. We show that increasing atmospheric CO2 concentrations can drive non-equilibrium decreases in N availability and cause the development of N limitation, while the effects of increased temperature appear to be relatively small and short-lived. These environmental changes may cause reductions in N availability over the vast areas of Earth that are not affected by high rates of atmospheric deposition and/or N enrichment associated with urban and agricultural land use.

The Leeward Kohala Field System (LKFS) on Hawai‘i Island once featured over 60 km2 of productive, rain-fed croplands. For several centuries, its occupants cultivated ‘uala (Ipomoea batatas, sweet potato) as a staple crop between kuaiwi (earthen or rock walls) planted with ko (Saccharum officinarum, sugarcane).These raised ko rows could have influenced ‘uala growth through an array of microclimatic processes, including wind abatement, shading, and the redistribution of moisture. While such effects are frequently mentioned in the literature, efforts to directly quantify them and relate them to ‘uala production have been lacking. We measured wind speeds, precipitation rates, solar illuminance, soil moisture, and ‘uala yields along a transect through three ko rows within the LKFS. Ko rows proved effective windbreaks, reducing near-surface wind speeds by up to 90% and for distances of up to 10 m. The rows also concentrated wind-blown moisture at their upwind edges while creating rain shadows 5–6 m in length. ‘Uala yields peaked at 3.8–6.0 kg m–2 near the center of inter-row space, probably because ‘uala were energy-limited during the wet study period and grew slowly when shaded by the ko. A zone of low turbulence leeward of each ko row also appeared to benefit ‘uala growth. Additional measurements are needed to investigate the landscape-level hydrologic effects of ko row planting. Our findings will help guide ongoing efforts to expand agricultural and educational activities in the LKFS.

Plant litter is a well-defined pool of organic matter in which the influence of Mn on decomposition (both decomposition rate, and the mix of compounds ultimately transferred to soil organic matter) has been clearly demonstrated in temperate forests. However, no similar study exists on grasslands, and the effect of foliar Mn versus soil-derived Mn on litter decomposition is poorly known. We used 5-month and 12-month field and 10-month laboratory experiments to evaluate organic-matter decomposition on the Kohala rainfall gradient in areas with different foliar and soil Mn abundances, and on which a single plant species dominates primary production and the litter pool. Chemical imaging analyses of decomposed litter revealed that Mn2+ oxidized to Mn3+ and Mn4+ on grass litter during decompositions—hallmarks of Mn-driven OM oxidation. However, these transformations and Mn abundance did not predict greater litter mass loss through decomposition. These observations demonstrate that the importance of Mn to an ecosystem’s C cycle does not rely solely on the metal’s abundance and availability.

Many degraded ecosystems have altered nutrient dynamics due to invaders’ possessing a suite of traits that allow them to both outcompete native species and alter the environment. In ecosystems where invasive species have increased nutrient turnover rates, it can be difficult to reduce nutrient availability. This study examined whether a functional trait‐based restoration approach involving the planting of species with conservative nutrient‐use traits could slow rates of nutrient cycling and consequently reduce rates of invasion. We examined a functional trait restoration initiative in a heavily invaded lowland wet forest site in Hilo, Hawaiʻi. Native and introduced species were chosen to create four experimental hybrid forest communities, in comparison to the invaded forest, with a factorial design in which communities varied in rates of carbon turnover (slow or moderate [SLOW, MOD]), and in the relationship of species in trait space (redundant or complementary [RED, COMP]). After the first 5 years, we evaluated community‐level outcomes related to nutrient cycling: carbon (C), nitrogen (N), and phosphorus (P) via litterfall, litter decomposition, and outplant productivity and rates of invasion. We found that (1) regardless of treatment, the experimental communities had low rates of nutrient cycling through litterfall relative to the invaded reference forest, (2) the MOD communities had greater nutrient release via litterfall than the SLOW communities, (3) introduced species had greater nutrient release than native species in the two MOD experimental communities, and (4) within treatments, there was a positive relationship between nutrient levels and outplant basal area, but outplant basal area was negatively associated with rates of invasion. The negative relationships among basal area and weed invasion, particularly for the two COMP treatments, suggest species existing in different parts of trait space may help confer some degree of invasion resistance. The diversification of trait space was facilitated by the use of introduced species, a new concept in Hawaiian forest management. Although challenges remain in endeavors to restore this heavily degraded ecosystem, this study provides evidence that functional trait‐based restoration approaches using carefully crafted hybrid communities can reduce rates of nutrient cycling and invasion in order to reach management goals.

Growing population and consumption pose unprecedented demands on food production. However, ammonia emissions mainly from food systems increase oceanic nitrogen deposition contributing to eutrophication. Here, we developed a long-term oceanic nitrogen deposition dataset (1970 to 2018) with updated ammonia emissions from food systems, evaluated the impact of ammonia emissions on oceanic nitrogen deposition patterns, and discussed the potential impact of nitrogen fertilizer overuse. Based on the chemical transport modeling approach, oceanic ammonia-related nitrogen deposition increased by 89% globally between 1970 and 2018, and now, it exceeds oxidized nitrogen deposition by over 20% in coastal regions including China Sea, India Coastal, and Northeastern Atlantic Shelves. Approximately 38% of agricultural nitrogen fertilizer was excessive, which corresponds to 15% of global oceanic ammonia-related nitrogen deposition. Policymakers and water quality managers need to pay increasingly more attention to ammonia associated with food production if the goal of reducing coastal nitrogen pollution is to be achieved for Sustainable Development Goals.

Manganese (Mn) exists as Mn(II), Mn(III), or Mn(IV) in soils, and the Mn oxidation state controls the roles of Mn in numerous environmental processes. However, the variations of Mn oxidation states with climate remain unknown. We determined the Mn oxidation states in highly weathered bulk volcanic soils (primary minerals free) across two rainfall gradients covering mean annual precipitation (MAP) of 0.25-5 m in the Hawaiian Islands. With increasing MAP, the soil redox conditions generally shifted from oxic to suboxic and to anoxic despite fluctuating at each site; concurrently, the proportions of Mn(IV) and Mn(II) decreased and increased, respectively. Mn(III) was low at both low and high MAP, but accumulated substantially, up to 80% of total Mn, in soils with prevalent suboxic conditions at intermediate MAP. Mn(III) was likely hosted in Mn(III,IV) and iron(III) oxides or complexed with organic matter, and its distribution among these hosts varied with soil redox potentials and soil pH. Soil redox conditions and rainfall-driven leaching jointly controlled exchangeable Mn(II) in soils, with its concentration peaking at intermediate MAP. The Mn redox chemistry was at disequilibrium, with the oxidation states correlating with long-term average soil redox potentials better than with soil pH. The soil redox conditions likely fluctuated between oxic and anoxic conditions more frequently at intermediate than at low and high MAP, creating biogeochemical hot spots where Mn, Fe, and other redox-sensitive elements may be actively cycled.