Nitrogen addition promotes terrestrial plants to allocate more biomass to aboveground organs: A global meta-analysis

A significant increase in reactive nitrogen (N) added to terrestrial ecosystems through agricultural fertilization or atmospheric deposition is considered to be one of the most widespread drivers of global change. Modifying biomass allocation is one primary strategy for maximizing plant growth rate, survival, and adaptability to various biotic and abiotic stresses. However, there is much uncertainty as to whether and how plant biomass allocation strategies change in response to increased N inputs in terrestrial ecosystems. Here, we synthesized 3516 paired observations of plant biomass and their components related to N additions across terrestrial ecosystems worldwide. Our meta-analysis reveals that N addition (ranging from 1.08 to 113.81 g m-2  year-1 ) increased terrestrial plant biomass by 55.6% on average. N addition has increased plant stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8%, 12.9%, and 13.4%, respectively, but with an associated decrease in plant reproductive mass (including flower and fruit biomass) fraction by 3.4%. We further documented a reduction in plant root-shoot ratio and root mass fraction by 27% (21.8%-32.1%) and 14.7% (11.6%-17.8%), respectively, in response to N addition. Meta-regression results showed that N addition effects on plant biomass were positively correlated with mean annual temperature, soil available phosphorus, soil total potassium, specific leaf area, and leaf area per plant. Nevertheless, they were negatively correlated with soil total N, leaf carbon/N ratio, leaf carbon and N content per leaf area, as well as the amount and duration of N addition. In summary, our meta-analysis suggests that N addition may alter terrestrial plant biomass allocation strategies, leading to more biomass being allocated to aboveground organs than belowground organs and growth versus reproductive trade-offs. At the global scale, leaf functional traits may dictate how plant species change their biomass allocation pattern in response to N addition.

Identifying older people in need using action research

An ageing population has implications for community-based health promotion and disease prevention. There is concern about older people who do not fit into existing programmes and services yet need minimal support to maintain independence. A study was designed to develop approaches to gain access to this hard to reach population, assess needs and design and test interventions to integrate them into the community. The study, informed by theories of health promotion and social support, used action research methods. Participant observation documented in field notes, together with case notes and clinical assessments, provided a rich source of qualitative and quantitative data. This article discusses the needs assessment. Over a 3-year period, public health nurses linked with community groups in a predominantly francophone, urban community to identify the target group. Key characteristics of the target group included limitations with instrumental activities of daily living and low levels of social support combined with stressful life situations that challenged adaptation. Three patterns of inadequate support were identified.