Agriculture Reference
In-Depth Information
addition to changes in fine-root density, morphology and structure, altera-
tions in root functioning are also frequently observed in the changed envi-
ronments. However, it has been a general observation that the long-lived
plants have more time to acclimate to changing environmental conditions
than the short-lived organisms. On a time scale, this acclimation might
occur in the order of several years. The acclimation process might be in-
fluenced by seasonal changes in environmental conditions.
1.3.2 IMPACT ON VEGETABLES
Increasing CO
2
will enhance photosynthesis and improve water-use ef-
ficiency, thus increasing yield in most vegetable crops. Relative benefits
from increased CO
2
can often be maintained with modest water and N de-
ficiency, but yield benefits on an absolute basis are reduced when water or
N limit growth. The impact of increasing temperatures is more difficult to
predict. Seed germination will probably be improved for most vegetables,
as will vegetative growth in regions where mean daily temperatures dur-
ing the growing season remain under 25 °C, assuming adequate water is
available. Reproductive growth is extremely vulnerable to periods of heat
stress in many important vegetable fruiting crops, such as tomato, pep-
per, bean and sweet corn, and yield reductions will probably occur unless
production is shifted to cooler portions of the year or to cooler production
regions. This vulnerability results from the shortened duration of grain,
storage tissue, or fruit filling and from failure of various reproductive
events, especially the production and release of viable pollen. Processing
crops, which are sometimes direct-seeded and are more frequently grown
in cool-summer areas, are more likely than fresh-market crops to benefit
from higher temperatures. In general, crops with a high harvest index, high
sink demand, indeterminate growth and long growth seasons are consid-
ered most likely to respond positively to the combination of higher CO
2
and temperature. Relatively few crops have been studied, however and
cultivars within a crop often differ in their responses, thus making gener-
alizations difficult.
In many crops, high temperatures may decrease quality parameters,
such as size, soluble solids and tenderness. For fresh-market vegetable
producers, even minor quality flaws can make their crops completely un-
saleable in some markets. Reduced or more irregular precipitation will also
