C. Chu

The effects of light and nitrogen on photosynthesis, leaf characteristics, and dry matter allocation in the chaparral shrub, Diplacus aurantiacus

SummaryPlants of Diplacus aurantiacus, a successional shrub common in California chaparral, were grown under controlled conditions in which either quantum flux density or nitrogen availability was varied. Photosynthesis and leaf nitrogen content were determined on a leaf area and a leaf weight basis, and whole plant growth was monitored.There was a direct relationship between photosynthesis and leaf nitrogen content on both area and weight bases. Reduced light intensity of the growth environment resulted in reductions in light-saturated photosynthesis and nitrogen content on an area basis, but not on a weight basis. With reduced nitrogen availability, photosynthesis and leaf nitrogen content per unit leaf weight decreased.Resource use efficiency increased as the resource became more limiting. The results are consistent with a model of plant growth in which net carbon gain of the leaf is maximized.

Seasonal carbon allocation in Heteromeles arbutifolia, a California evergreen shrub

SummaryThe seasonal patterning of carbon gain and allocation was studied in the California evergreen sclerophyll shrub, Heteromeles arbutifolia. Specifically an analysis was made of the seasonal structural allocations to stems, leaves, roots and reproductive parts as well as to functional categories of cell structure, metabolism, storage, and secondary compounds (predator protection).The differential partitioning during the various seasons is viewed in terms of the overall carbon economy of the shrub. It is suggested that not all functions can be met simultaneously, even though there is year round carbon gain, because of the heavy allocation demands to meet a particular environmental stress during a given season. For example, during the spring there is a priority allocation to the development of the canopy, apparently for competitive purposes, with little going to reproduction, storage and secondary compounds.

Compensating effects to growth of carbon partitioning changes in response to SO2-induced photosynthetic reduction in radish

SummaryExposure of plants to SO2 reduced their photosynthetic performance due tio reductions in carboxylating capacity. Although the reduced carbon gain resulted in a lower growth rate of SO2-exposed plants over that of controls, their loss of potential growth was minimized because of proportional increases in allocation to new leaf material.

Seed weight and seed resources in relation to plant growth rate

SummaryRelative growth rate in radish is not influenced by initial seed weight.

Allocation to reproduction in the chaparral shrub, Diplacus aurantiacus

SummaryThe semi-drought-deciduous shrub, Diplacus aurantiacus, allocates a large, relatively constant proportion of carbon and nitrogen to sexual reproduction. Experimental manipulation at a site in the chaparral of coastal central California showed that both reproduction and vegetative growth were strongly limited by water and little affected by shade or by addition of nutrients unless accompanied by water. Potential competition for carbon between growth and reproduction is reduced by photosynthesis within reproductive structures; competition is also constrained by localization of translocation. Results are discussed in relation to the hypothesis that allocation to reproduction in Diplacus has been selected to maximize reproductive success.

Stomatal responses to humidity of coastal and interior populations of a Californian shrub

SummaryPlants of two populations of Diplacus aurantiacus, a subshrub of the Californian chaparral, were compared for their stomatal response to water vapor concentration gradients. Plants of a coastal and an interior population were compared when grown under both low and high humidities. When grown at high humidity the coastal plants exhibited higher conductances and higher transpiration/photosynthesis ratios at all leaf-to-air water vapor concentration gradients than did the interior plants. Although all of the plants examined showed a pronounced stomatal response to humidity the response did not result in the degree of regulation of water-use efficiency reported for other Californian coastal species.

Carbohydrate, water and nitrogen storage in vines of a tropical deciduous forest

Between the mid dry season and the early wet season nine vine species representing diverse root-, stem-, and leafhabits and phenological patterns, showed more differences among plant parts in their contents of non-structural carbohydrate, water, and nitrogen, than within the parts. Most seasonal changes occurred in distal stems, while none occurred in roots. Carbohydrates differed least between seasons, despite reserves of 3-15 percent in stems and up to 50 percent in roots.

The seasonal dynamics of leaf resin, nitrogen, and herbivore damage in Eriodictyon californicum and their parallels in Diplacus aurantiacus

SummaryThe chaparral shrub Eriodictyon californicum produces a flavonoid leaf resin with a chemically similar composition to that previously reported for the sympatric shrub Diplacus aurantiacus. We determined the phenology, resin content, and nitrogen content of Eriodictyon leaves and the leaf area lost to herbivores. Nitrogen content and resin content were both negatively correlated with leaf age at each sampling date, but nitrogen decreased during the growing season while resin increased. The fraction of leaf area lost during the growing season averaged less than 7% and was highest on the oldest leaves. The seasonal pattern of resin production in Eriodictyon corresponds to that in Diplacus, indicating that the similar environments of Eriodyctyon and Diplacus have led to convergent leaf resins. This convergence in these two plants has implications for chemicals of similar function in other chaparral shrubs.