## 3 Results and Discussion
### Duration between Gas Exchange Measurements of In Situ Leaves  
Comparison of gas exchange measurement times of _in situ_ and excised grape leaves from field experiments conducted over a number of years gave a clear perspective of sample size and time between consecutive measurements of grapevine gas exchange (Table 2). Gas exchange measured on _in situ_ leaves over four years (2006, 2008, 2009, and 2010) on six _V. vinifera_ cultivars (Carignon, Merlot, Grenache, Cabernet Sauvignon, Pinot noir, and Mourvedre) yielded a total of 2388 sample data points (Table 2). Excised leaves measured over three years (2016, 2017, and 2018) across four cultivars (Cabernet Sauvignon, Grenach, Malbec, and Pinot gris) produced 710 data points (Table 2). Statistical analysis revealed about a third less time was required to complete two consecutive measurements on excised leaves (57.52 \(\pm\) 0.39 s) compared to _in situ_ (86.96 \(\pm\) 0.41 s) (Table 2). Based upon these results, we affirm a significant difference in time between excised and _in situ_ treatments (_p_ < 0.001) (Table 2). The mean transpired time for the excision treatment was about 30 s faster when compared to mean transpired time for the _in situ_ treatment. This implies that on a typical day of gas exchange measurement (\(\pm\)2 h of solar noon) about 250 data points could be recorded using leaf excision technique as opposed to 165 data points using _in situ_ leaves. The time saved described in our experiment is situational and depends on experimental design, distance between plots, number of individuals taking measurements, etc. However, leaf excision could be a feasible option in specific experimental conditions such as vineyards, greenhouses, or growth chambers where vines are tightly spaced. Measurement times observed in our experiment were similar to previous research conducted on ornamental tree species such as Shantung map (_Acer truncatum_), Mexican redbud (_Cercis canadensis_ var. _mexicana_), Texas redbud (_C. canadensis_ var. _texensis_), white Texas redbud (_C. canadensis_ var. _texensis_ cv Alba), Oklahoma redbud (_C. canadensis_ var. _texensis_ cv Oklahoma), Chinquapin oak (_Quercus muhelenbergii_), and English oak (_Q. robur_) [1; 2; 3]. A reduced period between consecutive measurements observed in the excision data compared to _in situ_ data indicates an opportunity for researchers to increase the number of sample leaf gas exchange measurements over the same period of time, and thus increase  
Figure 2: Net CO\({}_{2}\) assimilation (\(A_{\mathrm{n}}\)) vs. stomatal conductance (\(g_{\mathrm{s}}\)) for five grape (_Vitis vinifera_) cultivars: Cabernet franc (**A**); Cabernet Sauvignon (**B**); Chardonnay (**C**); Grenache (**D**); and Tempranillo (**E**) under excision treatment. Lines are the best fit (\(\alpha\) = 0.05). Regression equations and R\({}^{2}\) values were shown within each panel. Each symbol represents the mean of 16 measurements. sample size. Greater sample size is crucial in determining data patterns [32], and developing accurate explanatory models [33]. Leaf excision techniques have previously been used by various researchers to measure leaf gas exchange parameters [7; 34; 35]. However, these reports did not focus on the potential benefits of increased sample size. Although our current study is comparable to a previous experiment [3] accuracy of the technique will likely depend upon species, experimental design, plant water status, environmental conditions, leaf position, cultivar, etc. In addition, our results should not be considered a benchmark, and representative or comparable to grapevine leaf gas exchange results from past, or future experiments. Thus, as is standard practice, leaf gas exchange levels from a single research experiment should not be directly compared to other experiments. Results should be examined and compared only to data collected and analyzed within each individual experiment.