Halstead, S.J., G.P. Robertson, K.L. Gross, M. Halvorson, and R.R. Harwood
Presented at the All Scientist Meeting (1996-07-16 to 1996-07-17 )
Net primary productivity (NPP) estimates provide an important component in understanding the flow of carbon and energy through ecosystems. Aboveground net primary productivity (ANPP) is measured at the KBS LTER in habitats ranging from annual cropping systems to deciduous forests.The diverse plant communities in these habitats require different harvest and/or sampling methods. All measurements are taken pre-harvest at peak annual biomass for the major community components. This generally means physiological maturity for annuals and pre-senescence for perennials; most treatments are thus sampled at least twice per year depending on the life history of community components (e.g. wheat Vs winter annuals in T1) and on agronomic harvest frequency (e.g. 4 times per year for alfalfa). If possible, biomass samples are taken from each of five sampling stations within the hectare plot, although labor, weather, and time constraints may alter the number of sampling stations for a given harvest.For treatments 1- 8 and the SF (successional field) ANPP is assessed by harvesting all the above ground portion of plants rooted within the bounds of the harvest quadrat. Clipped plants are bagged and stored at 4 C until botanical separations are performed. Harvested plants are separated by species and identified using the five letter Bayer code system. Crops are further separated into seed and stover. Plants are dried at 60 C for a minimum of 48 h and dry weights recorded, along with the date of harvest, field replicate, treatment, sampling station and species code. In the poplar systems (T5), wood biomass estimates are derived using basal diameter measurements in relation to allometric equations developed from whole-tree harvest on site. For the forested (CF and DF) sites, wood growth increments are measured with dendrometers bands on trees with > 10 cm dbh. Dendrometers were installed in the summer of 1995 and woody increment growth will be available in the fall of 1996. Leaf production in sites with trees is estimated with leaf litter traps placed on the forest floor.Aboveground net primary productivity (ANPP) for 1995 differed considerably between treatments (Figure 1). ANPP in the perennial cropping systems, T5 poplars and T6 alfalfa, far exceeded biomass as the annual cropping systems or the successional treatments. Annual poplar wood production was twice that of wheat biomass and four times greater than successional vegetation production. Productivity in the annual cropping systems, T1-T4 wheat, did not differ between conventional and notill management and was lower for plots with low (T3) or zero chemical input (T4). Successional field biomass (T7, T8, and T-SF) varied greatly across sites and was highest in grass dominated plots. Annual wood production and forest understory composition and biomass in the DF and CF treatments will be measured beginning in 1996.
Back to meeting | Show |