Day‐to‐day variation in nitrogenase activity of Alnus incana explained by weather variables: a multivariate time series analysis

Abstract

A modelling system is described that indicates the extent to which day‐to‐day variations in nitrogenase activity in young Alnus incana (L.) Moench, grown in defined conditions in the field, may be affected by weather conditions both during and prior to the day of measurement. Nitrogenase activity (acetylene reduction activity, ARA) was measured weekly on intact field‐grown grey alder (A. incana) plants, 0.15–0.42 m tall at planting, nodulated with Frankia. The measurements were done at noon on two groups of plants in 1987 and on two other groups in 1988. Each group was made up of five or six plants. Seven weather variables: daily sunshine hours, daily mean, maximum and minimum air temperature, daily mean and 1300 h relative humidity, and daily rainfall were used. The relation between log(ARA/leaf area) and the weather variables were analysed using a PLS model (partial least squares projection to latent structures). The advantage of PLS is that it can handle x‐variables that are correlated. Data from 1987 were chosen as a training set. Multivariate PLS time series analysis was made by adding, in a stepwise manner, the weather data up to 5 d before the day of measurement. This procedure gave six models with n * 7 x‐variables (n= 1–6). With the models from the time series analysis of 1987 data, true predictions of ARA per leaf area were made from weather data 1988 (test set 1) and from ‘early‐season’ weather data from 1987 and 1988 (test set 2). The variation in ARA/leaf area could be predicted from the weather conditions. The predictions of the two test sets improved when the weather conditions one and two days before the day of measurements were added to the model. The further addition of weather data from 3 to 5 d before the day of measurement did not improve the model. The good predictions of ARA/leaf area show that the alders responded to the variable weather conditions in the same way in 1988 as in 1987, despite the ten‐fold difference in size (leaf area) at the end of the growing season. Among the weather variables, air temperature and the daily sunshine hours were positively correlated to ARA, while relative air humidity and rainfall were negatively correlated to ARA. The daily minimum temperature and rainfall appeared to have least impact on ARA. By use of PLS, we could extract information out of a data set containing highly correlated x‐variables, information that is non‐accessible with conventional statistical tools such as multiple regression. When making measurements of nitrogenase activities under field conditions, we propose that attention should be paid to the weather conditions on the days preceding the day of measurement. The day‐to‐day variation in nitrogenase activity is discussed with reference to known effects of stress factors under controlled conditions.

Diurnal and seasonal patterns of nitrogen fixation in analnus hirsuta plantation of central Korea

“…Our values were lower than those reported by Binkley et al, 19945-40 52-155 Sharma et al, 200215-20 130 Binkley, 198115-20 20 Binkley, 1981 common in that study region (Binkley et al, 1992). Howevel, seasonal changes in photoassimilates might also have influenced acetylene reduction rates (Wheeler, 1971 ;Tripp et al, 1979;Huss-Danell et al, 1992;Ekblad et al, 1994). Soil moisture content was low between spring and early summer (range of 3.7 to 13.6%), but rapidly increased and remained high from mid-summer throughout the rest of the season (26.5 to 28.2%).…”

Forest soil respiration rate and ?13C is regulated by recent above ground weather conditions

“…In conclusion, there is more and more evidence suggesting that soil temperature does not exert the major control on the rate of root/rhizosphere/mycorrhizal respiration in trees and that, in analogy with root respiration and root growth in grasslands (Craine et al 1998;Fitter et al 1998), and nitrogenase activity in A. incana (Ekblad et al 1994), the rate of tree root respiration is dependent on the availability of recently produced photosynthates Ho¨gberg et al 2001;Bhupinderpal-Singh et al 2003). It is well known that weather variables like air humidity and air temperature have a profound impact on the rate of net photosynthesis (Lambers et al 1998).…”

“…Studies of grasslands show that root respiration correlated to the previous 2 days, and root growth to the previous 10 days cumulative radiation flux (Fitter et al 1998). Studies of field grown A. incana showed the dayto-day variation in nitrogenase activity to be dependent on the previous 2 days above ground weather conditions (Ekblad et al 1994). As suggested by Bowling et al (2002), the lag time between photosynthesis and respiration may vary over the season depending on several abiotic and biotic factors.…”

“…Its use in biology is increasing. Examples are the prediction of photoinhibition in willow leaves in the field from photosynthetic photon flux density (PPFD) measurements (Ö gren and Sjo¨stro¨m 1990), the prediction of day-to-day variations in nitrogenase activity of Alnus incana from above ground weather data (Ekblad et al 1994), and the prediction of soil microbial variables from wet chemical analyses and pyrolysis GC/MS data (Palmborg et al 1998). One disadvantage is that PLS cannot be used to create simple models, as is made with multiple regression analysis.…”

Nitrogen fixation by Alnus incana and nitrogen transfer from A. incana to Pinus sylvestris influenced by macronutrients and ectomycorrhiza

“…At high nitrogen availability, or other forms of stress, a decrease in nodule specific activity is to be expected (HussDanell. 1990; see also discussion in Ekblad et al, 1994 andEkblad, 1995). Our results agree with the idea that nitrogen fixation is regulated by the plant's growth and nitrogen demand (Tjepkema, Schwintzer & Benson, 1986;Parsons et al, 1993).…”