In line with the current series of threads looking into plant sciences, I thought it valuable to offer some background reading material that some may find interesting
https://agrilifecdn.tamu.edu/briske/fil ... PTER95.pdf
It is a bit of a hefty read but some interesting statements in summery from page 60
Summary statements
1. Steady-state plant growth is immediately disrupted by defoliation in response to a
substrate limitation imposed by a reduction in photosynthetic area. A reduction in
whole-plant photosynthesis and preferential carbon allocation to active shoot sinks
reduces root growth and nutrient absorption as root carbohydrates are depleted.
The extent to which these physiological processes are suppressed and their
potential rates of recovery directly affect the grazing resistance, competitive ability
and productivity of defoliated plants.
2. The reduction of carbohydrate pools within root systems following defoliation
primarily results from the combined effects of a reduction in the amount of
photosynthetic carbon allocated to the root system and the continued utilization of
carbohydrates in root respiration, rather than the remobilization of carbohydrates to
support shoot regrowth. Although, carbohydrate pools within the remaining shoot
system are important for initiating plant growth when photosynthetic capacity is
severely limited, the relative inaccessibility of root carbohydrates to support shoot
growth, the limited amount of carbohydrates stored in tiller bases, and poor
correlations between shoot regrowth and carbohydrate concentrations or pools
limits their use as an effective index of shoot regrowth in perennial grasses and
potentially other growth forms as well.
61
3. Compensatory photosynthesis is a very consistent physiological response following
defoliation that has been documented in numerous species. The process involves
the rejuvenation of leaves and/or the postponement of the normal decline in
photosynthetic capacity that occurs as leaves age and senesce. Although the
occurrence of compensatory photosynthesis is partially influenced by increased
light availability following partial canopy removal, indirect mechanisms presumably
mediated by cytokinins or other root produced signals, appears to be the
predominant mechanism inducing the response. Compensatory photosynthesis
occurs in defoliation-sensitive as well as defoliation-tolerant species and it often
does not persist throughout the recovery period. Therefore, the rate of leaf area
expansion following defoliation plays a greater role than does the increase in
photosynthetic rate per unit leaf area in the reestablishment of whole-plant
photosynthetic capacity.
4. Canopy reestablishment is a function of the source, number, and activity of
remaining meristems; the availability of photosynthetic carbon, and the amount of
stored carbohydrates and nutrients. Growth following defoliation is most rapid from
intercalary meristems, intermediate from apical meristems and slowest from axillary
buds. Canopy reestablishment is delayed when a large portion of the active
meristems are removed by defoliation, or when suboptimal environmental
conditions or intense competition limit growth, photosynthesis, or nutrient
acquisition. A series of compensatory processes, including increased resource
allocation to shoots, increased photosynthetic rates, and enhanced rates of nutrient
absorption by roots, may occur within several days of defoliation to increase
relative growth rates over those of undefoliated plants.
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